1,677 results on '"Local density of states"'
Search Results
2. Bandstructure and quantum transport properties of AGNR unit cells with V-shaped edge patterning.
- Author
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Basumatary, Bikramjit and Mathew, Agile
- Abstract
We investigate how the electronic and transport properties of six arm-chair graphene nanoribbon-based structures are modified with the introduction of symmetrical and asymmetrical geometrical V-cuts on their edges. A tight-binding model based on numerical non-equilibrium Green's function method is used to compute the transport properties such as local density of states, transmission and current–voltage characteristics. We report the existence of nearly flat mid-bands for certain topologies after edge patterning. These bands give rise to non-zero transmission at low bias voltages. We uncover how this transmission varies with width, length, and biasing of the channel and also the temperature of the contacts. For structures in which flat mid-bands are absent, we show how their band gaps could be tuned by varying the width and length of the modified unit cells. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
3. Inverse design in quantum nanophotonics: combining local-density-of-states and deep learning
- Author
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Liu Guang-Xin, Liu Jing-Feng, Zhou Wen-Jie, Li Ling-Yan, You Chun-Lian, Qiu Cheng-Wei, and Wu Lin
- Subjects
deep learning ,entanglement dynamics ,inverse design ,local density of states ,nanophotonics ,spontaneous emission dynamics ,Physics ,QC1-999 - Abstract
Recent advances in inverse-design approaches for discovering optical structures based on desired functional characteristics have reshaped the landscape of nanophotonic structures, where most studies have focused on how light interacts with nanophotonic structures only. When quantum emitters (QEs), such as atoms, molecules, and quantum dots, are introduced to couple to the nanophotonic structures, the light–matter interactions become much more complicated, forming a rapidly developing field – quantum nanophotonics. Typical quantum functional characteristics depend on the intrinsic properties of the QE and its electromagnetic environment created by the nanophotonic structures, commonly represented by a scalar quantity, local-density-of-states (LDOS). In this work, we introduce a generalized inverse-design framework in quantum nanophotonics by taking LDOS as the bridge to connect the nanophotonic structures and the quantum functional characteristics. We take a simple system consisting of QEs sitting on a single multilayer shell–metal–nanoparticle (SMNP) as an example, apply fully-connected neural networks to model the LDOS of SMNP, inversely design and optimize the geometry of the SMNP based on LDOS, and realize desirable quantum characteristics in two quantum nanophotonic problems: spontaneous emission and entanglement. Our work introduces deep learning to the quantum optics domain for advancing quantum device designs; and provides a new platform for practicing deep learning to design nanophotonic structures for complex problems without a direct link between structures and functional characteristics.
- Published
- 2023
- Full Text
- View/download PDF
4. Maximum electromagnetic local density of states via material structuring
- Author
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Chao Pengning, Kuate Defo Rodrick, Molesky Sean, and Rodriguez Alejandro
- Subjects
fundamental limits ,inverse design ,local density of states ,purcell enhancement ,Physics ,QC1-999 - Abstract
The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications.
- Published
- 2022
- Full Text
- View/download PDF
5. Dynamic control of spontaneous emission using magnetized InSb higher-order-mode antennas
- Author
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Sina Aghili, Rasoul Alaee, Amirreza Ahmadnejad, Ehsan Mobini, Mohammadreza Mohammadpour, Carsten Rockstuhl, and Ksenia Dolgaleva
- Subjects
active antenna ,indium antimonide (InSb) ,local density of states ,multipole moments ,radiative decay rate ,Zeeman-splitting effect ,Applied optics. Photonics ,TA1501-1820 ,Optics. Light ,QC350-467 - Abstract
We exploit InSb’s magnetic-induced optical properties to design THz sub-wavelength antennas that actively tune the radiative decay rates of dipole emitters at their proximity. The proposed designs include a spherical InSb antenna and a cylindrical Si-InSb hybrid antenna demonstrating distinct behaviors. The former dramatically enhances both radiative and non-radiative decay rates in the epsilon-near-zero region due to the dominant contribution of the Zeeman-splitting electric octupole mode. The latter realizes significant radiative decay rate enhancement via magnetic octupole mode, mitigating the quenching process and accelerating the photon production rate. A deep-learning-based optimization of emitter positioning further enhances the quantum efficiency of the proposed hybrid system. These novel mechanisms are promising for tunable THz single-photon sources in integrated quantum networks.
- Published
- 2024
- Full Text
- View/download PDF
6. Maximum electromagnetic local density of states via material structuring.
- Author
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Chao, Pengning, Kuate Defo, Rodrick, Molesky, Sean, and Rodriguez, Alejandro
- Subjects
DENSITY of states ,HEAT radiation & absorption ,PHOTONICS ,CONSERVATION of energy ,ENERGY conservation - Abstract
The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
7. Unveiling atom-photon quasi-bound states in hybrid plasmonic-photonic cavity
- Author
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Lu Yu-Wei, Zhou Wen-Jie, Li Yongyao, Li Runhua, Liu Jing-Feng, Wu Lin, and Tan Haishu
- Subjects
atom-photon quasi-bound states ,local density of states ,plasmonic-photonic cavity ,Physics ,QC1-999 - Abstract
Dissipation, often associated with plasmons, leads to decoherence and is generally considered fatal for quantum nonlinearities and entanglement. Counterintuitively, by introducing a dissipative plasmonic nanoantenna into a typical cavity quantum electrodynamics (QED) system, we unveil the wide existence of the atom-photon quasi-bound state (qBS), a kind of exotic eigenstate with anomalously small decay, in the hybrid plasmonic-photonic cavity. To derive the analytical condition of atom-photon qBS, we formulate a quantized two-mode model of the local density of states by connecting the interacting uncoupled cavity modes to the macroscopic QED. With resonant plasmon-photon coupling, we showcase the single-atom qBS that improves the efficiency of single-photon generation over one order of magnitude; and the two-atom qBS that significantly enhances spontaneous entanglement generation compared with a bare photonic cavity. Notably, such single-atom and multi-atom qBS can be simultaneously accessed in realistic plasmonic-photonic cavities, providing a versatile platform for advanced quantum technologies, such as quantum light sources, quantum computation, and quantum information.
- Published
- 2022
- Full Text
- View/download PDF
8. First–Principles Calculations of Band Offsets in GaAs/AlAs System
- Author
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Seiyed Hamid Reza Shojaei and Mahmoud Oloumi
- Subjects
nanosemiconductors ,density functional theory ,band discontinuities ,pseudopotential ,local density of states ,Science - Abstract
The lattice-matched system (GaAs)n/(AlAs)n superlattice is calculated for two different values of n=3 and 6 within ab initio pseudopotential density-functional theory using Quantum Espresso package of program exploiting the ultra-soft atomic pseudopotentials. Their band offsets, which is a well-known and inextricable problem at semiconductor interfaces, have been determined in this paper and were compared with experimental results. Discontinuities of valance and conduction bands were obtained as 0.46 and 0.25 eV, respectively. The averaged self-consistent potential across the [001] interface in GaAs is about 0.061 eV higher than its value in AlAs. The local density of states for both superlattices was also studied. The effect of different factors e.g. orientation, transitivity, and composition dependence is reported in this study. We found that, in the [110] direction of GaAs/AlAs superlattice, the dependence of the band offset on the orientation is negligible. The calculated band gap of is linearly dependent on aluminum content.
- Published
- 2022
- Full Text
- View/download PDF
9. An energy-resolved atomic scanning probe.
- Author
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Gruss, Daniel, Chien, Chih-Chun, Barreiro, Julio T, Di Ventra, Massimiliano, and Zwolak, Michael
- Subjects
Affordable and Clean Energy ,quantum transport ,cold atoms ,scanning probe ,local density of states ,cond-mat.mes-hall ,cond-mat.quant-gas ,quant-ph ,Physical Sciences ,Fluids & Plasmas - Abstract
We propose a method to probe the local density of states (LDOS) of atomic systems that provides both spatial and energy resolution. The method combines atomic and tunneling techniques to supply a simple, yet quantitative and operational, definition of the LDOS for both interacting and non-interacting systems: It is the rate at which particles can be siphoned from the system of interest by a narrow energy band of non-interacting states contacted locally to the many-body system of interest. Ultracold atoms in optical lattices are a natural platform for implementing this broad concept to visualize the energy and spatial dependence of the atom density in interacting, inhomogeneous lattices. This includes models of strongly correlated condensed matter systems, as well as ones with non-trivial topologies.
- Published
- 2018
10. Super-resolution imaging: when biophysics meets nanophotonics
- Author
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Koenderink A. Femius, Tsukanov Roman, Enderlein Jörg, Izeddin Ignacio, and Krachmalnicoff Valentina
- Subjects
fluorescence-lifetime imaging microscopy ,local density of states ,localization artifacts ,metal-induced energy transfer ,quantum yield ,single-molecule localization microscopy ,Physics ,QC1-999 - Abstract
Probing light–matter interaction at the nanometer scale is one of the most fascinating topics of modern optics. Its importance is underlined by the large span of fields in which such accurate knowledge of light–matter interaction is needed, namely nanophotonics, quantum electrodynamics, atomic physics, biosensing, quantum computing and many more. Increasing innovations in the field of microscopy in the last decade have pushed the ability of observing such phenomena across multiple length scales, from micrometers to nanometers. In bioimaging, the advent of super-resolution single-molecule localization microscopy (SMLM) has opened a completely new perspective for the study and understanding of molecular mechanisms, with unprecedented resolution, which take place inside the cell. Since then, the field of SMLM has been continuously improving, shifting from an initial drive for pushing technological limitations to the acquisition of new knowledge. Interestingly, such developments have become also of great interest for the study of light–matter interaction in nanostructured materials, either dielectric, metallic, or hybrid metallic-dielectric. The purpose of this review is to summarize the recent advances in the field of nanophotonics that have leveraged SMLM, and conversely to show how some concepts commonly used in nanophotonics can benefit the development of new microscopy techniques for biophysics. To this aim, we will first introduce the basic concepts of SMLM and the observables that can be measured. Then, we will link them with their corresponding physical quantities of interest in biophysics and nanophotonics and we will describe state-of-the-art experiments that apply SMLM to nanophotonics. The problem of localization artifacts due to the interaction of the fluorescent emitter with a resonant medium and possible solutions will be also discussed. Then, we will show how the interaction of fluorescent emitters with plasmonic structures can be successfully employed in biology for cell profiling and membrane organization studies. We present an outlook on emerging research directions enabled by the synergy of localization microscopy and nanophotonics.
- Published
- 2021
- Full Text
- View/download PDF
11. Surface Conductivity and Preferred Orientation of TiN Film for Ti Bipolar Plate.
- Author
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Yan, Zhi, Li, Tao, Wang, Qian, Li, Hongjiao, Wang, Yao, Wu, Chaoling, Yan, Yigang, and Chen, Yungui
- Subjects
SURFACE conductivity ,TITANIUM nitride ,REACTIVE sputtering ,THIN films ,MAGNETRON sputtering ,LOW temperatures - Abstract
The properties of thin films are often influenced by the crystal's preferred orientation. In the present study, we report the strong dependence of surface conductivity on the preferred orientation of TiN film that acts as the coating material for Ti bipolar plate. The preferred orientation of TiN film is successfully controlled along the (111) or (200) planes by adjusting the N
2 flow rate or Ti substrate temperature during the deposition process via DC (direct current) reactive magnetron sputtering. Small N2 flow rate of 3 to 6 sccm or low substrate temperature (e.g., 25 °C) facilitates the growth of TiN films along the (111). The (111) preferred orientated TiN films show much lower interfacial contact resistance (ICR) than the (200) preferred orientated films. A considerably low ICR value of 1.9 mΩ·cm2 at 140 N/cm2 is achieved at the N2 flow of 4 sccm and the substrate temperature of 25 °C. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
12. Super-resolution imaging: when biophysics meets nanophotonics.
- Author
-
Koenderink, A. Femius, Tsukanov, Roman, Enderlein, Jörg, Izeddin, Ignacio, and Krachmalnicoff, Valentina
- Subjects
HIGH resolution imaging ,BIOPHYSICS ,NANOPHOTONICS ,ATOMIC physics ,QUANTUM electrodynamics ,NEAR-field microscopy - Abstract
Probing light–matter interaction at the nanometer scale is one of the most fascinating topics of modern optics. Its importance is underlined by the large span of fields in which such accurate knowledge of light–matter interaction is needed, namely nanophotonics, quantum electrodynamics, atomic physics, biosensing, quantum computing and many more. Increasing innovations in the field of microscopy in the last decade have pushed the ability of observing such phenomena across multiple length scales, from micrometers to nanometers. In bioimaging, the advent of super-resolution single-molecule localization microscopy (SMLM) has opened a completely new perspective for the study and understanding of molecular mechanisms, with unprecedented resolution, which take place inside the cell. Since then, the field of SMLM has been continuously improving, shifting from an initial drive for pushing technological limitations to the acquisition of new knowledge. Interestingly, such developments have become also of great interest for the study of light–matter interaction in nanostructured materials, either dielectric, metallic, or hybrid metallic-dielectric. The purpose of this review is to summarize the recent advances in the field of nanophotonics that have leveraged SMLM, and conversely to show how some concepts commonly used in nanophotonics can benefit the development of new microscopy techniques for biophysics. To this aim, we will first introduce the basic concepts of SMLM and the observables that can be measured. Then, we will link them with their corresponding physical quantities of interest in biophysics and nanophotonics and we will describe state-of-the-art experiments that apply SMLM to nanophotonics. The problem of localization artifacts due to the interaction of the fluorescent emitter with a resonant medium and possible solutions will be also discussed. Then, we will show how the interaction of fluorescent emitters with plasmonic structures can be successfully employed in biology for cell profiling and membrane organization studies. We present an outlook on emerging research directions enabled by the synergy of localization microscopy and nanophotonics. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
13. Complete asymptotic expansions of the spectral function for symbolic perturbations of almost periodic Schrödinger operators in dimension one.
- Author
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Galkowski, Jeffrey
- Subjects
SCHRODINGER operator ,ASYMPTOTIC expansions ,DIFFERENTIAL operators ,OPERATOR functions ,CALCULUS - Abstract
In this article we consider asymptotics for the spectral function of Schrödinger operators on the real line. Let PW
L2 (R) ! L².R/have the form P:= - d²/dx² C W; where W is a self-adjoint first order differential operator with certain modified almost periodic structure. We show that the kernel of the spectral projector,- Shterenberg and Sobolev with Melrose's scattering calculus. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
14. Local density of states in a one-dimensional photonic crystal with a semiconducting cavity
- Author
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Francis Segovia-Chaves, Herbert Vinck-Posada, and E. Petrovish Navarro-Barón
- Subjects
Photonic crystal ,Local density of states ,Dyadic Green’s functions ,Pressure ,Photonic band gaps ,Physics ,QC1-999 - Abstract
In this paper, we calculate the local density of states using dyadic Green’s functions for a defective one-dimensional photonic crystal of finite size composed of alternating air and semiconductor layers. Herein, spatial periodicity is broken as one of the semiconductor layers increases its layers. In this study, we consider that the refractive index of semiconductor materials, such as GaAs, Si, and SiO2, changes with the amount of the applied pressure. We determined the existence of a confined mode within the cavity with a maximum value of the local density of states. The results show that, as pressure increases, the local density of states decreases within the confined mode. However, for the GaAs cavity, the results reveal that increased pressure favors the appearance of a larger number of confined modes at frequencies within the second photonic band gaps.
- Published
- 2022
- Full Text
- View/download PDF
15. Surface Contribution to Thermodynamic Properties of Solids.
- Author
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RAM, P. N., KUSHWAHA, M., and CHATTERJEE, A. KUMAR
- Subjects
- *
ATOMIC spectra , *FREQUENCY spectra , *GREEN'S functions , *POINT defects , *SOLIDS , *SPECIFIC heat , *TUNGSTEN alloys , *PHONONIC crystals - Abstract
We present an approach based on local representation of frequency spectrum to calculate the surface contribution to thermodynamic properties of solids. The Green function theory of isolated point defects is discussed in detail which is also applicable to vibrations of surface atoms. The expression for local spectra of atoms is obtained in terms of the same site Green functions. The surface contribution to thermodynamic properties of solids is expressed in terms of the local frequency spectra of atoms in a few surface layers and the frequency spectrum of the infinite crystal satisfying the cyclic boundary condition. The usefulness of the formulation along with the ability of the recursion method to calculate local spectra without a recourse to detailed frequency calculations of slabs is emphasized. As an illustrative example, we present the surface contribution to low temperature lattice specific heat of tungsten due to (100) surface. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
16. Giant enhancement of emission intensity by using microcavity
- Author
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Muhammad Hanif Ahmed Khan Khushik and Chun Jiang
- Subjects
Emission intensity ,Local density of states ,Branching ratio ,Band of interest ,Physics ,QC1-999 - Abstract
We propose theoretically a tunable circular Bragg microcavity to enhance the intensity of the emission band of interest in rare-earth-doped materials and to suppress the unwanted emission bands which produce noise and diminish the efficiency of the emission of interest. The surrounding of the microcavity comprises of alternating layers of high-index and low-index materials. The luminescent ions such as neodymium Nd3+ having different emission bands in different host materials are placed in the microcavity, and single emission band with stronger intensity can be observed, and other emission bands are suppressed. The wavelength of the single emission peak can be changed from one wavelength to other wavelengths by varying the refractive index, radius of the microcavity and thus modifying the local density of states of the microcavity. The fluorescence branching ratio of emission band of interest can be enhanced from 10% to 100% due to suppression of the unwanted emission bands.
- Published
- 2020
- Full Text
- View/download PDF
17. Supporting information of: Effect of the effective refractive index on the radiative decay rate in nanoparticle thin films [Dataset]
- Author
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European Research Council, European Commission, Fundación BBVA, Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación (España), Romero Aguilar, Manuel [0000-0002-7594-1361], Sánchez-Valencia, J. R. [0000-0003-2493-4433], Lozano, Gabriel [0000-0002-0235-4924], Míguez, Hernán [0000-0003-2925-6360], Romero Aguilar, Manuel [manuel.romero@csic.es], Lozano, Gabriel [g.lozano@csic.es], Míguez, Hernán [h.miguez@csic.es], Romero Aguilar, Manuel, Sánchez-Valencia, J. R., Lozano, Gabriel, Míguez, Hernán, European Research Council, European Commission, Fundación BBVA, Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación (España), Romero Aguilar, Manuel [0000-0002-7594-1361], Sánchez-Valencia, J. R. [0000-0003-2493-4433], Lozano, Gabriel [0000-0002-0235-4924], Míguez, Hernán [0000-0003-2925-6360], Romero Aguilar, Manuel [manuel.romero@csic.es], Lozano, Gabriel [g.lozano@csic.es], Míguez, Hernán [h.miguez@csic.es], Romero Aguilar, Manuel, Sánchez-Valencia, J. R., Lozano, Gabriel, and Míguez, Hernán
- Abstract
In this work, we theoretically and experimentally study the influence of the optical environment on the radiative decay rate of luminescent nanoparticles forming a thin film. We use electric dipole sources in finite-difference time-domain simulations to analyze the effect of modifying the effective refractive index of transparent layers made of phosphor nanocrystals doped with rare earth cations, and propose a significant correction to previously reported analytical models for calculating the radiative decay rate. Our predictions are tested against an experimental realization of such films, in which we manage to vary the effective refractive index in a gradual and controllable manner. Our model accurately accounts for the measurements attained, allows us discriminating the radiative and non-radiative contributions to the time-resolved photoluminescence, and provides a way to rationally tune the spontaneous decay rate and hence the photoluminescence quantum yield of an ensemble of nanoparticles.
- Published
- 2023
18. Transport in quantum dots resonant tunneling diodes in non-interacting regime
- Author
-
M T Asefpour and P Sahebsara
- Subjects
resonant tunnelling diode ,Green function ,quantum dots ,transport ,local density of states ,Physics ,QC1-999 - Abstract
In this paper, we used green's function approach in microscopic theory to investigate a resonant tunneling diode (RTD). We introduced the detailed Hamiltonian for each part of the photovoltaic p-i-n system, then by calculating the green's function components in tight-binding approximation, we calculate local density of states and current-voltage characteristic of the p-i-n structure. Our results show a non-Ohmic behavior and negative differential resistance in RTD. As a result of a longitudinal electric field, the local density of states varies by changing the applied potential. Moreover, we study the effect of changing the physical parameters on the current of the device. Entering quantum dots in the middle of device causes a negative differential resistance, which is a consequence of resonant tunneling phenomenon.
- Published
- 2017
19. Isotope engineering of near-field radiative thermal diodes.
- Author
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Xie, Lanyi and Song, Bai
- Subjects
- *
DIODES , *PHONONS , *ISOTOPES , *ENGINEERING design , *THIN films - Abstract
• Isotope engineering of near-field thermal diodes is explored for the first time. • Over 20% rectification enhancement is predicted for a wide parameter space. • At experimentally friendly gaps around 400 nm, 6-fold enhancement is possible. • Isotope-induced SPhP line shift and broadening are the key physical mechanisms. • Two guidelines for isotope engineering are proposed and supported with examples. Guided by a rational design approach centering on the electromagnetic local density of states (LDOS), we explore the potential of isotopically engineering radiative thermal diodes for enhanced rectification with a focus on the near field. Based on fluctuational electrodynamics, we theoretically demonstrate that for thermal diodes pairing thin films of intrinsic silicon (i -Si) and lithium hydride (LiX), the rectification ratio can increase by over six times with varying isotopic compositions. This is because by leveraging the isotope-induced shift and broadening of the surface phonon polaritons in LiX, more LDOS contrast provided by i -Si can be effectively converted into thermal rectification. Moreover, we show that such improvement is fairly robust, as evidenced by the prediction of over 20% rectification enhancement across a wide physical and geometric parameter space. Finally, inspired by insights from the i -Si-based thermal diodes, we propose general guidelines for implementing isotope engineering in the design of practical devices, which are further illustrated via representative diodes employing vanadium dioxide and silicon carbide as the active materials. Our work highlights the efficacy of isotopes in boosting the performance of radiative thermal diodes, which also holds promise for broader applications such as thermal transistors, thermal switches, and thermophotovoltaics. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
20. Direct observation of intrinsic surface magnetic disorder in amorphous superconducting films
- Author
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Idan Tamir, Martina Trahms, Franzisca Gorniaczyk, Felix von Oppen, Dan Shahar, and Katharina J. Franke
- Subjects
Electronic structure ,500 Naturwissenschaften und Mathematik::530 Physik::539 Moderne Physik ,Condensed Matter - Superconductivity ,Thin films ,Evaporation ,FOS: Physical sciences ,Sputtering ,Local density of states ,equipment and supplies ,Condensed Matter::Disordered Systems and Neural Networks ,Superconducting gap ,Liquid helium cooling ,Superconductivity (cond-mat.supr-con) ,Amorphous materials ,Scanning tunneling spectroscopy ,Condensed Matter::Superconductivity ,Superconducting phase transition ,Impurities in superconductors ,human activities ,Low-temperature superconductors - Abstract
The interplay between disorder and interactions can dramatically influence the physical properties of thin-film superconductors. In the most extreme case, strong disorder is able to suppress superconductivity as an insulating phase emerges. Due to the known pair-breaking potential of magnetic disorder on superconductors, the research focus is on the influence of non-magnetic disorder. Here we provide direct evidence that magnetic disorder is also present at the surface of amorphous superconducting films. This magnetic disorder is present even in the absence of magnetic impurity atoms and is intimately related to the surface termination itself. While bulk superconductivity survives in sufficiently thick films, we suggest that magnetic disorder may crucially affect the superconductor-to-insulator transition in the thin-film limit.
- Published
- 2023
- Full Text
- View/download PDF
21. Control of the emission of elementary quantum systems using metamaterials and nanometaparticles
- Author
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Vasily Klimov
- Subjects
Physics ,Local density of states ,Nanostructure ,Field (physics) ,business.industry ,Physics::Optics ,General Physics and Astronomy ,Metamaterial ,Quantum dot ,Optoelectronics ,business ,Quantum ,Plasmon ,Quantum computer - Abstract
The most important direction in the development of fundamental and applied physics is the study of the properties of optical systems at nanoscales for creating optical and quantum computers, biosensors, single-photon sources for quantum informatics, DNA sequencing devices, detectors of various fields, etc. In all these cases, nanosize light sources such as dye molecules, quantum dots (epitaxial or colloidal), color centers in crystals, and nanocontacts in metals are of utmost importance. In the nanoenvironment, the characteristics of these elementary quantum systems—pumping rates, radiative and nonradiative decay rates, the local density of states, lifetimes, level shifts—experience changes, which can be used to create nanosize light sources with the desired properties. Modern theoretical and experimental works on controlling the emission of elementary quantum systems with the help of plasmonic and dielectric nanostructures, metamaterials, and metamaterial nanoparticles are analyzed.
- Published
- 2021
- Full Text
- View/download PDF
22. Effect of Contact Geometry on Spin Transport in Amine-Ended Single-Molecule Magnetic Junctions
- Author
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Yu Hui Tang and Kuan Rong Chiang
- Subjects
Materials science ,Local density of states ,General Chemical Engineering ,Fermi energy ,General Chemistry ,Ring (chemistry) ,Article ,Bond length ,Chemistry ,Covalent bond ,Chemical physics ,Molecule ,HOMO/LUMO ,QD1-999 ,Spin-½ - Abstract
We employ the first-principles calculation with non-equilibrium Green's function method to comprehensively investigate the crucial role of interfacial geometry in spin transport properties of Co/1,4-benzenediamine (BDA)/Co single-molecule magnetic junctions (SMMJs). Two bonding mechanisms are proposed for the hard-hard Co-N coupling: (1) the covalent bonding between the H-dissociated amine linker and spin-polarized Co apex atoms and (2) the dative interaction between the H-non-dissociated (denoted by +H) amine linker and Co apex atoms. The former covalent contact dominates the π-resonance interfacial spin selection that can be well preserved in H-dissociated cases regardless of the choice of top, bridge, and hollow contact sites. From our detailed analyses of spin-polarized transmission spectra, local density of states, and molecular density of states, the underlying mechanism is that the strong hybridization between Co-d, N-p y , and the π-orbital of the phenyl ring in dissociated cases renders the 2-fold HOMO (4-fold LUMO) of the central molecule closer to the Fermi energy. In contrast, the enlarged Co-N bond length of the latter dative contact in the H-non-dissociated case not only destroys the spinterface coupling but also blocks the spin injection. This theoretical work may provide vital and practical insights to illustrate the spin transport property in real amine-ended SMMJs since the contact geometries and interfacial bond mechanisms remain unclear during the breaking junction technique.
- Published
- 2021
23. Full orbital decomposition of Yu-Shiba-Rusinov states based on first principles
- Author
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German Research Foundation, European Commission, Ministerio de Economía y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), Generalitat de Catalunya, Johannes Gutenberg University Mainz, Saunderson, Tom G., Annett, James F., Csire, Gábor, Gradhand, Martin, German Research Foundation, European Commission, Ministerio de Economía y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), Generalitat de Catalunya, Johannes Gutenberg University Mainz, Saunderson, Tom G., Annett, James F., Csire, Gábor, and Gradhand, Martin
- Abstract
We have implemented the Bogoliubov-de Gennes equation in a screened Korringa-Kohn-Rostoker method for solving, self-consistently, the superconducting state for three-dimensional (3D) crystals including substitutional impurities. In this paper we extend this theoretical framework to allow for collinear magnetism and apply it to fcc Pb with 3D magnetic impurities. In the presence of magnetic impurities, there is a pair-breaking effect that results in in-gap Yu-Shiba-Rusinov (YSR) states which we decompose into contributions from the individual orbital character. We determine the spatial extent of these impurity states, showing how the different orbital character affects the details of the YSR states within the superconducting gap. Our work highlights the importance of a first-principles-based description which captures the quantitative details, making direct comparisons with experimental findings possible.
- Published
- 2022
24. Spin-polarized gate-tuned transport property of a four-terminal MoS2 device: a theoretical study
- Author
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Guiling Zhang, Hong Yan, Hong Yu, Lei Pei, and Yan Shang
- Subjects
Materials science ,OR gate ,Local density of states ,Condensed matter physics ,Terminal (electronics) ,Mechanics of Materials ,Scattering ,Mechanical Engineering ,Nanowire ,Conductance ,General Materials Science ,Density functional theory ,Spin-½ - Abstract
The transport property of a four-terminal MoS2NR/V7(Bz)8 device is computed within the framework of density functional theory combined with the nonequilibrium Green’s function (NEGF) technique. This device is constructed by a MoS2 nanoribbon (MoS2NR) as the source-to-drain channel and a spin-polarized V7(Bz)8 nanowire grafted on the MoS2NR surface as the double gate channel, where the four terminals are all connected to a semi-infinite one-dimensional (1D) Au lead. The transport characteristic is explored by investigating the conductance, currents, local density of states (LDOS), and scattering states. The currents of different leads are dissimilar due to the complex interplay between the four terminals that is otherwise not present in a two-terminal setup. The most interesting feature we articulate is that the induced promising properties including negative differential resistance (NDR) behavior, input/output current switching, as well as spin-polarized lead currents can be fine-tuned by the magnitude of either source bias or gate bias. These features can be utilized in designing multi-terminal nanoelectronic devices.
- Published
- 2021
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25. Universal lasing condition
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Evgeny S. Andrianov, Alexander Pukhov, I. V. Doronin, Alexander Vinogradov, Yurii E. Lozovik, and Alexander A. Zyablovsky
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Electromagnetic field ,Science ,Physics::Optics ,02 engineering and technology ,Radiation ,Purcell effect ,01 natural sciences ,Article ,law.invention ,Optics ,law ,0103 physical sciences ,Lasers, LEDs and light sources ,Emission spectrum ,010306 general physics ,Physics ,Quantum optics ,Multidisciplinary ,Local density of states ,business.industry ,021001 nanoscience & nanotechnology ,Laser ,Physics::Accelerator Physics ,Medicine ,0210 nano-technology ,business ,Lasing threshold ,Coherence (physics) - Abstract
Usually, the cavity is considered an intrinsic part of laser design to enable coherent emission. For different types of cavities, it is assumed that the light coherence is achieved by different ways. We show that regardless of the type of cavity, the lasing condition is universal and is determined by the ratio of the width of the atomic spectrum to the product of the number of atoms and the spontaneous radiation rate in the laser structure. We demonstrate that cavity does not play a crucial role in lasing since it merely decreases the threshold by increasing the photon emission rate thanks to the Purcell effect. A threshold reduction can be achieved in a cavity-free structure by tuning the local density of states of the electromagnetic field. This paves the way for the design of laser devices based on cavity-free systems.
- Published
- 2021
26. Decoupling the metal insulator transition and crystal field effects of VO2
- Author
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In-Hui Hwang, Sunmog Yeo, Chang-In Park, Cheng-Jun Sun, and Sang-Wook Han
- Subjects
Materials science ,Science ,Analytical chemistry ,02 engineering and technology ,01 natural sciences ,Article ,Ion ,Crystal ,Electrical resistance and conductance ,0103 physical sciences ,Metal–insulator transition ,010306 general physics ,Multidisciplinary ,Local density of states ,Extended X-ray absorption fine structure ,Physics ,021001 nanoscience & nanotechnology ,X-ray absorption fine structure ,K-edge ,Medicine ,0210 nano-technology ,human activities ,circulatory and respiratory physiology - Abstract
VO2 is a highly correlated electron system which has a metal-to-insulator transition (MIT) with a dramatic change of conductivity accompanied by a first-order structural phase transition (SPT) near room temperature. The origin of the MIT is still controversial and there is ongoing debate over whether an SPT induces the MIT and whether the Tc can be engineered using artificial parameters. We examined the electrical and local structural properties of Cr- and Co-ion implanted VO2 (Cr-VO2 and Co-VO2) films using temperature-dependent resistance and X-ray absorption fine structure (XAFS) measurements at the V K edge. The temperature-dependent electrical resistance measurements of both Cr-VO2 and Co-VO2 films showed sharp MIT features. The Tc values of the Cr-VO2 and Co-VO2 films first decreased and then increased relative to that of pristine VO2 as the ion flux was increased. The pre-edge peak of the V K edge from the Cr-VO2 films with a Cr ion flux ≥ 1013 ions/cm2 showed no temperature-dependent behavior, implying no changes in the local density of states of V 3d t2g and eg orbitals during MIT. Extended XAFS (EXAFS) revealed that implanted Cr and Co ions and their tracks caused a substantial amount of structural disorder and distortion at both vanadium and oxygen sites. The resistance and XAFS measurements revealed that VO2 experiences a sharp MIT when the distance of V–V pairs undergoes an SPT without any transitions in either the VO6 octahedrons or the V 3d t2g and eg states. This indicates that the MIT of VO2 occurs with no changes of the crystal fields.
- Published
- 2021
27. Correlation-driven topological phases in magic-angle twisted bilayer graphene
- Author
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Alex Thomson, Yang Peng, Robert Polski, Kenji Watanabe, Harpreet Singh Arora, Hyun-Jin Kim, Cyprian Lewandowski, Takashi Taniguchi, Yiran Zhang, Jason Alicea, Stevan Nadj-Perge, and Youngjoon Choi
- Subjects
Physics ,Multidisciplinary ,Local density of states ,Magic angle ,media_common.quotation_subject ,Fermi level ,Fermi surface ,Landau quantization ,Topology ,01 natural sciences ,Asymmetry ,010305 fluids & plasmas ,symbols.namesake ,0103 physical sciences ,symbols ,010306 general physics ,Electronic band structure ,Bilayer graphene ,media_common - Abstract
Magic-angle twisted bilayer graphene (MATBG) exhibits a range of correlated phenomena that originate from strong electron-electron interactions. These interactions make the Fermi surface highly susceptible to reconstruction when ±1, ±2 and ±3 electrons occupy each moire unit cell, and lead to the formation of various correlated phases1-4. Although some phases have been shown to have a non-zero Chern number5,6, the local microscopic properties and topological character of many other phases have not yet been determined. Here we introduce a set of techniques that use scanning tunnelling microscopy to map the topological phases that emerge in MATBG in a finite magnetic field. By following the evolution of the local density of states at the Fermi level with electrostatic doping and magnetic field, we create a local Landau fan diagram that enables us to assign Chern numbers directly to all observed phases. We uncover the existence of six topological phases that arise from integer fillings in finite fields and that originate from a cascade of symmetry-breaking transitions driven by correlations7,8. These topological phases can form only for a small range of twist angles around the magic angle, which further differentiates them from the Landau levels observed near charge neutrality. Moreover, we observe that even the charge-neutrality Landau spectrum taken at low fields is considerably modified by interactions, exhibits prominent electron-hole asymmetry, and features an unexpectedly large splitting between zero Landau levels (about 3 to 5 millielectronvolts). Our results show how strong electronic interactions affect the MATBG band structure and lead to correlation-enabled topological phases.
- Published
- 2021
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- View/download PDF
28. NixInSe (0001) Metal-Semiconductor Heteronanosystem Study.
- Author
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Galiy, P. V., Nenchuk, T. M., Ciszewski, A., Mazur, P., Yarovets, I. R., and Dveriy, O. R.
- Subjects
CRYSTALS ,SCANNING electron microscopy ,SPECTRUM analysis ,SIMULATION methods & models ,NANOSTRUCTURED materials - Abstract
Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2017
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29. Cold and Hot Spots: From Inhibition to Enhancement by Nanoscale Phase Tuning of Optical Nanoantennas
- Author
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Pietro Lombardi, Nicola Palombo Blascetta, Niek F. van Hulst, and Costanza Toninelli
- Subjects
Materials science ,near field interference ,Phase (waves) ,Physics::Optics ,Bioengineering ,Hot spot (veterinary medicine) ,single molecule ,plasmonics ,Interference (communication) ,General Materials Science ,Plasmon ,antenna enhancement ,Local density of states ,Física [Àrees temàtiques de la UPC] ,local density of states ,business.industry ,Mechanical Engineering ,Detector ,hot spot - cold spot ,General Chemistry ,Condensed Matter Physics ,nanoantennas ,local phase ,Optoelectronics ,nanoantenna ,inhibition of emission ,Antenes ,Antenna (radio) ,business ,superresolution ,Excitation - Abstract
Optical nanoantennas are well-known for the confinement of light into nanoscale hot spots, suitable for emission enhancement and sensing applications. Here, we show how control of the antenna dimensions allows tuning the local optical phase, hence turning a hot spot into a cold spot. We manipulate the local intensity exploiting the interference between driving and scattered field. Using single molecules as local detectors, we experimentally show the creation of subwavelength pockets with full suppression of the driving field. Remarkably, together with the cold excitation spots, we observe inhibition of emission by the phase-tuned nanoantenna. The fluorescence lifetime of a molecule scanned in such volumes becomes longer, showing slow down of spontaneous decay. In conclusion, the spatial phase of a nanoantenna is a powerful knob to tune between enhancement and inhibition in a 3-dimensional subwavelength volume.
- Published
- 2020
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- View/download PDF
30. Electronic band structure of silver low-index surfaces: a tight-binding study
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D. Olguín, A. Rubio-Ponce, and H.J. Herrera-Suárez
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Physics ,Index (economics) ,Local density of states ,010304 chemical physics ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Tight binding ,Transition metal ,0103 physical sciences ,0210 nano-technology ,Electronic band structure - Abstract
We studied the electronic band structure and corresponding local density of states of low-index fcc Ag surfaces (100), (110), and (111) by using the empirical tight-binding method in the framework of the Surface Green’s Function Matching formalism. The energy values for different surface and resonance states are reported and a comparison with the available experimental and theoretical data is also done.
- Published
- 2020
- Full Text
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31. On the characterization of topological phases of matter via local density of states and boundary charge
- Author
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M��ller, Niclas, Schoeller, Herbert, and Kennes, Dante Marvin
- Subjects
boundary charge ,condensed matter physics ,topology ,local density of states ,condensed matter physics , topology , low-dimensional systems , local density of states , boundary charge ,low-dimensional systems ,ddc:530 - Abstract
Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2022). = Dissertation, RWTH Aachen University, 2022, The last decades have witnessed the rise of topology, which became one of the dominating paradigms in condensed matter physics. From a theoretical perspective, the focus often lies on topological invariants which, through the bulk-boundary correspondence can be used to predict the presence of edge states at the surfaces of insulating materials. These edge states are believed to be integral in the advancement of future technologies, such as quantum computation, microelectronics and spintronics. This thesis contributes to the field of topological phases of matter by reporting research results concerning the characterization of the latter using two complementary approaches: an energy-resolved, local density of states approach and an energy-unresolved, boundary charge approach. With respect to the first approach, we demonstrate how the local density of states, as computed using the Keldysh Green���s function formalism, can be used to model trans-port experiments in tight-binding models and how to identify topological edge states in the resulting data. As a testbed for this approach we study models of one-dimensional, periodically driven (Floquet) topological insulators and two-dimensional higher order topological superconductors. The findings in this regard are twofold. Firstly, we show how, in the case of the Floquet model, contrary to the local density of states approach, the topological invariants are not able to distinguish between degenerate edge states with vastly different localization lengths, rendering the invariant practically meaning-less. Secondly, while the simulations generally agree with the predictions made using topological considerations, we demonstrate how bulk effects can skew the picture and should therefore be kept in mind when interpreting experimental results. We identify the origin of the aforementioned bulk effects with nontopological edge states, argue for the universality of these states and analytically examine them in the context of the Floquet model and a generalized Kitaev chain, which we identify as the simplest model to feature said states. The second approach to the characterization of topological phases of matter that we discuss is based on the concept of the boundary charge. This experimentally accessible quantity is defined as the charge that accumulates at the surface of an insulator. At zero temperature, it can be thought of as the integrated (up to the chemical potential) excess electronic density, and thus lacks the energy resolution which is essential in detecting the subtle bulk effects mentioned above. Since it generally contains contributions from both localized edge states and extended bulk states, its analysis with respect to the topology of the phase in question is highly nontrivial. We show how the boundary charge can be divided into contributions stemming from bulk states, edge states and from the polarization of the unit cell respectively. We propose novel, boundary charge based invariants, which are given in terms of winding numbers of bulk Green���s functions and which are applicable to all insulating systems, irrespective of symmetry constraints. We demonstrate their validity using randomly generated one-dimensional models. The scope of this thesis lies in the demonstration that the topological invariant approach yields an incomplete picture in certain circumstances, necessitating the use of further theoretical tools, such as those discussed in the following., Published by RWTH Aachen University, Aachen
- Published
- 2022
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32. Enhancing Coupling of Electromagnetic Waves with Artificial Materials
- Author
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Guclu, Caner
- Subjects
Electrical engineering ,Electromagnetics ,absorber ,anistoropic media ,composite ,hyperbolic media ,local density of states ,metamaterial - Abstract
Metamaterials are composites that are engineered purposefully for realizing electromagnetic characteristics that do not occur naturally in mineral or organic form. These characteristics are realized by regular arrangements of meta atoms, the building blocks of metamaterials, that mimic the atoms in an element. The electric and magnetic responses of these building blocks are engineered in such a way that the effective permittivity and permeability of metamaterials can be tuned. Similarly, the anisotropy of constitutive electromagnetic parameters can also be controlled efficiently. This dissertation focuses on the enhancement of the interaction between light and matter using bulk anisotropic metamaterials and magnetic meta atoms, in order to enhance, control and/or isolate electric and magnetic nature of emitters. This is achieved first through utilization of hyperbolic metamaterials (HMs) which are a subcategory of uniaxially anistotropic materials exhibiting opposite signs of permittivity or permeability along and orthogonal the axis of anisotropy. HMs host a wide spatial spectrum of propagating waves, i.e., high gradient field features can be transferred in HMs owing to the propagating waves in ideally indefinitely large spatial spectrum. Optical HMs are mainly constructed by periodic alternating layers of plasmonic metals and dielectrics. The power emitted by point sources (and arrays of point sources) in the vicinity of HMs is highly boosted compared to regular dielectric media. Moreover, most of the power is absorbed by the HM. Similar characteristics can be realized using graphene layers instead of metals in the infrared regime, where the chemical potential can be an effective means of controlling emission enhancement. Thereafter, a reactively loaded transmission line grid is presented as an example of a two-dimensional HMs, where the canalization of large spectral waves leads to transferring high resolution features. HMs can also be molded into resonators that provide high-quality resonances even in subwavelength dimensions. These extraordinary resonances are demonstrated to boost radiative emission of dipolar emissions. Another exotic property of anisotropic metamaterials is investigated with near-zero permittivity conditions where huge electric field enhancements are achieved in larger intensities than those demonstrated using isotropic near-zero permittivity materials. Lastly, a circular cluster of plasmonic nanospheres under azimuthally polarized vector beams are studied as a way of boosting local magnetic field and isolating it from electric field, which is promising for studying weak magnetic transitions in high frequency range.
- Published
- 2016
33. An energy-resolved atomic scanning probe
- Author
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Daniel Gruss, Chih-Chun Chien, Julio T Barreiro, Massimiliano Di Ventra, and Michael Zwolak
- Subjects
quantum transport ,cold atoms ,scanning probe ,local density of states ,Science ,Physics ,QC1-999 - Abstract
We propose a method to probe the local density of states (LDOS) of atomic systems that provides both spatial and energy resolution. The method combines atomic and tunneling techniques to supply a simple, yet quantitative and operational, definition of the LDOS for both interacting and non-interacting systems: it is the rate at which particles can be siphoned from the system of interest by a narrow energy band of non-interacting states contacted locally to the many-body system of interest. Ultracold atoms in optical lattices are a natural platform for implementing this broad concept to visualize the energy and spatial dependence of the atom density in interacting, inhomogeneous lattices. This includes models of strongly correlated condensed matter systems, as well as ones with non-trivial topologies.
- Published
- 2018
- Full Text
- View/download PDF
34. Local density of states and scattering rates across the many-body localization transition
- Author
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Atanu Jana, V. Ravi Chandra, and Arti Garg
- Subjects
Physics ,Local density of states ,Strongly Correlated Electrons (cond-mat.str-el) ,Field (physics) ,Scattering ,FOS: Physical sciences ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Molecular physics ,Condensed Matter - Strongly Correlated Electrons ,Delocalized electron ,Scattering rate ,Phase (matter) ,Probability distribution ,Quantum - Abstract
Characterizing the many-body localization (MBL) transition in strongly disordered and interacting quantum systems is an important issue in the field of condensed matter physics. We study the single particle Green's functions for a disordered interacting system in one dimension using exact diagnonalization in the infinite temperature limit and provide strong evidence that single particle excitations carry signatures of delocalization to MBL transition. In the delocalized phase, the typical values of the local density of states and the scattering rate are finite while in the MBL phase, the typical values for both the quantities become vanishingly small. The probability distribution functions of the local density of states and the scattering rate are broad log-normal distributions in the delocalized phase while the distributions become very narrow and sharply peaked close to zero in the MBL phase. We also study the eigenstate Green's function for all the many-body eigenstates and demonstrate that both, the energy resolved typical scattering rate and the typical local density of states, can track the many-body mobility edges., Comment: A few changes to the text to improve clarity. No change in results. Close to the published version
- Published
- 2021
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- View/download PDF
35. Thermal near-field energy density and local density of states in topological one-dimensional Su-Schrieffer-Heeger chains and two-dimensional Su-Schrieffer-Heeger lattices of plasmonic nanoparticles
- Author
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Svend-Age Biehs, Zhenghua An, Achim Kittel, and Annika Ott
- Subjects
Physics ,Plasmonic nanoparticles ,Phase transition ,Dipole ,Local density of states ,Field (physics) ,Isotropy ,Near and far field ,Topology ,Measure (mathematics) - Abstract
We derive a general expression for the electric and magnetic part of the near-field energy density of $N$ dipoles of temperatures ${T}_{1},...,{T}_{N}$ immersed in a background field having a different temperature ${T}_{b}$. In contrast to former expressions this inclusion of the background field allows for determining the energy density of heated or cooled isotropic dipolar objects within an arbitrary environment which is thermalized at a different temperature. Furthermore, we show how the energy density is related to the local density of states. We use this general expression to study the near-field enhanced energy density at the edges and corners of one-dimensional (1D) Su-Schrieffer-Heeger chains and 2D Su-Schrieffer-Heeger lattices of plasmonic InSb nanoparticles when the phase transition from a topological trivial to a topological nontrivial state is made. We discuss the robustness of these modes when adding defects and the possibility to measure the topological edge and corner modes.
- Published
- 2021
- Full Text
- View/download PDF
36. Numerical analysis of transmission coefficient, LDOS, and DOS in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling MODFETs.
- Author
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Bouguenna, D., Wecker, T., As, D., Kermas, N., and Beloufa, A.
- Abstract
Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling modulation-doped field-effect transistors (MODFETs) using $$\hbox {next}{} \mathbf{nano}^{3}$$ software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green's function formalism, which has been integrated into the $$\hbox {next}\mathbf{nano}^{3}$$ software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}$$ on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of $$x = 20\,\%$$ of barrier layers, cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ superlattice nanostructures with very high density of states of 407 $$\hbox {eV}^{-1}$$ at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
37. Ab-initio studies on the electronic properties of Fe dopant in GaAs(1 1 0) surface.
- Author
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Fang, Zhou and Yi, Zhijun
- Subjects
- *
GALLIUM arsenide , *DOPING agents (Chemistry) , *ELECTRONIC structure , *VALENCE bands , *SCANNING tunneling microscopy , *SEMICONDUCTOR doping - Abstract
Using the first principles ground state method, the electronic properties of single Fe dopant in bulk and GaAs(1 1 0) surface are studied. Our calculations show that on-site correlations have significant effects on local geometrical and electronic structures for both bulk GaAs and GaAs(1 1 0) surface. Both t 2 g and e g orbitals of Fe impurity are split by on-site correlations and surface effects. Moreover, our calculated local density of states (LDOS), topography of in-gap states and valence band states based on DFT + U method agree well with experiments. Our calculated LDOS for Fe impurity on the GaAs(1 1 0) surface presents several electronic states above and below the Fermi level, and these states can be well interpreted with the hybridization between Fe 3d orbitals and p-like orbitals of host atoms. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
38. Effects of band hybridization on electronic properties in tuning armchair graphene nanoribbons.
- Author
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Khatun, M., Kan, Z., Cancio, A., and Nelson, C.
- Subjects
- *
GRAPHENE , *NANORIBBONS , *ELECTRONIC band structure , *ELECTRIC admittance , *GREEN'S functions - Abstract
We explore a model of armchair graphene nanoribbons tuned by functionalizing the edge states. Edge modifications are modeled by changing the electronic energy of the edge states in specific periodic patterns. The model can be considered to mimic a controlled doping process with different elements. The band structure, density of states, conductance, and local density of states are calculated, using the tight binding approach, Green's function methodology, and the Landauer formula. The results show interesting behaviors, which are considerably different from the properties of the perfect nanoribbons. The hybridization of conducting bands with non-conducting bands, which appear perfectly flat in the perfect ribbon, opens up and modifies gaps in conductance near the Fermi level. One particular pattern of edge functionalization causes a strong, symmetric, and systematic band gap change about the Fermi level, modifying the electronic characteristics in the energy dispersion, density of states, local density of states, and conductance. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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39. Exploring Fundamental Limits of Quantum Efficiency Measurements Using Quantum Electrodynamics
- Author
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Benson, Oliver, Balasubramanian, Kannan, Menezes, Leonardo de Souza, Özelci, Ersan, Benson, Oliver, Balasubramanian, Kannan, Menezes, Leonardo de Souza, and Özelci, Ersan
- Abstract
Photolumineszenz-Techniken spielen eine wichtige Rolle bei der Charakterisierung verschiedener funktionaler Fluorophore in den Lebens- und Materialwissenschaften, in der Biologie und bis hin zu den Quantentechnologien. Ein entscheidender und wichtiger Parameter für den Vergleich von Fluorophoren ist die Quanteneffizienz, die ein direktes Maß für die Umwandlungseffizienz von absorbierten Photonen in emittierte Photonen darstellt. Diese Größe charakterisiert die Nutzbarkeit von Emittern für Anwendungen in optischen Geräten, Einzelphotonenquellen und im biomedizinischen Bereich. Mehrere Techniken wie optische und photothermische Methoden werden verwendet, um die photolumineszente Quanteneffizienz zu messen, und so die Eignung von Fluorophoren für verschiedene Anwendungen zu bewerten. Quanteneffizienz-Messungen können jedoch eine Herausforderung für hochverdünnte Fluorophore sein, die in dünne Schichten eingebettet sind. Die in dieser Arbeit beschriebene Forschung überwindet die Herausforderungen der Quanteneffizienzmessung durch eine Modifikation der Wechselwirkung zwischen Licht und Umgebung., Photoluminescence techniques play an important role for characterization of various functional fluorophores in the life and material sciences from biology to quantum technologies. A crucial and key parameter for comparing the performance of fluorophores is the photoluminescence quantum efficiency or quantum yield, which presents a direct measure of conversion efficiency of absorbed photons into emitted photons. This quantity characterizes the performance of emitters for applications in optical devices as single photon sources and in the biomedical sector. Several techniques such as optical and photothermal methods are used to measure the photoluminescence quantum efficiency of emitters in various environments and aggregation states. Quantum efficiency measurements can be challenging for fluorophores in solid matrix, in scattering systems and for highly diluted fluorophores embedded to thin films. The research described in this thesis overcomes these challenges by performing quantum efficiency measurement via modifying the spontaneous emission as a fundamental process of light-matter interaction.
- Published
- 2021
40. Relativistic first-principles theory of Yu-Shiba-Rusinov states applied to Mn adatoms and Mn dimers on Nb(110)
- Author
-
Ministry of Innovation and Technology (Hungary), Ministerio de Economía y Competitividad (España), European Commission, Ministerio de Ciencia, Innovación y Universidades (España), Generalitat de Catalunya, Nyári, Bendegúz, Lászlóffy, András, Szunyogh, László, Csire, Gábor, Park, Kyungwha, Újfalussy, Balázs, Ministry of Innovation and Technology (Hungary), Ministerio de Economía y Competitividad (España), European Commission, Ministerio de Ciencia, Innovación y Universidades (España), Generalitat de Catalunya, Nyári, Bendegúz, Lászlóffy, András, Szunyogh, László, Csire, Gábor, Park, Kyungwha, and Újfalussy, Balázs
- Abstract
We present a fully relativistic first-principles-based theoretical approach for the calculation of the spectral properties of magnetic impurities on the surface of a superconducting substrate, providing a material specific framework for the investigation of the Yu-Shiba-Rusinov (YSR) states. By using a suitable orbital decomposition of the local densities of states we discuss in great detail the formation of the YSR states for an Mn adatom and for two kinds of Mn dimers placed on the Nb(110) surface and compare our results to recent experimental findings. In the case of the adatom we find that the spin-orbit coupling slightly shifts some of the YSR peaks and also the local spin polarization on the Nb atoms has marginal effects on their positions. Moreover, by scaling the exchange field on the Mn site we could explain the lack of the dx2−y2-like YSR state in the spectrum. While our results for a close packed ferromagnetic dimer are in satisfactory agreement with the experimentally observed splitting of the YSR states, in the case of an antiferromagnetic dimer we find that the spin-orbit coupling is not sufficiently large to explain the splitting of the YSR states seen in the experiment. Changing the relative orientation of the magnetic moments in this dimer induces splitting of the YSR states and also shifts their energy, leading even to the formation of a zero bias peak in the case of the deepest YSR state.
- Published
- 2021
41. Position dependence of local density of states in 3D band gap of a finite photonic crystal
- Author
-
Anna C. Tasolamprou, Maria Kafesaki, Costas M. Soukoulis, Thomas Koschny, Willem L. Vos, Eleftherios N. Economou, Shakeeb Bin Hasan, Charalampos P. Mavidis, Complex Photonic Systems, and MESA+ Institute
- Subjects
Physics ,Crystal ,Dipole ,Local density of states ,Condensed matter physics ,Band gap ,Position (vector) ,Condensed Matter::Superconductivity ,Physics::Optics ,Quantum information ,Quantum information science ,Photonic crystal - Abstract
Three dimensional photonic crystals offer the possibility to completely inhibit the local density of states (LDOS) for emitters inside the crystal [1] allowing the control of the LDOS which is crucial for emission control, quantum information science, photovoltaics and many more. However, total inhibition is completely true only for crystals of infinite size, whereas real devices are finite. Therefore, it is important to investigate the role of thr position and the dipole orientation of sources inside finite three-dimensional photonic crystals.
- Published
- 2021
42. 3 Ways to View the Local Density of Optical States
- Author
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Willem L. Vos, William L. Barnes, Simon A. R. Horsley, Complex Photonic Systems, and MESA+ Institute
- Subjects
Quantum optics ,Physics ,Range (mathematics) ,Theoretical physics ,Local density of states ,Electromagnetic Phenomena ,Nanophotonics ,Stimulated emission ,Focus (optics) ,Equivalence (measure theory) - Abstract
The concept of the local density of optical states (widely referred to as "LDOS") is ubiquitous in nanophotonics as it serves to explain a wide range of electromagnetic phenomena, varying from antenna physics [1] , fluorescence [2] - [4] and emission control [5] , [6] , inter-molecular energy transfer [7] , [8] , and strong coupling [9] . Recently, we explored the fundamentals of this concept and its consequences in a broad didactic overview [10] . Here, we focus in greater detail on one of the wide-ranging implications from our study, namely our newly gained insights of how one can view the local density of states in several different ways. Each of these different approaches offers an alternative conceptual insight into the local density of optical states. Importantly, by making a detailed comparison between the different approaches we show the equivalence of rather different research fields, namely electrical engineering, quantum optics, and nanophotonics viewpoints.
- Published
- 2021
43. Single-molecule imaging of LDOS modification by an array of plasmonic nanochimneys
- Author
-
Valentina Krachmalnicoff, Arturo Susarrey-Arce, Ignacio Izeddin, Yannick De Wilde, Guillaume Blanquer, Bart van Dam, Dirk Jonker, R. Margoth Cordova-Castro, Mesoscale Chemical Systems, and MESA+ Institute
- Subjects
Physics ,Atmospheric measurements ,Local density of states ,Position (vector) ,Electromagnetic environment ,business.industry ,Optoelectronics ,Nanometre ,business ,Single Molecule Imaging ,Plasmon ,Common emitter - Abstract
The direct measurement of a single emitter decay rate and the simultaneous knowledge of their position is a powerful tool for the study of light-matter interaction at the nanometer scale. In particular, the decay rate is directly related to the local density of states (LDOS) which measures the number of modes of the electromagnetic environment available for the decay of an emitter.
- Published
- 2021
44. Unveiling the multilevel structure of midgap states in Sb-doped MoX2 (X=S, Se, Te) monolayers
- Author
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Saif Ullah and Marcos G. Menezes
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Materials science ,Local density of states ,Condensed matter physics ,Dopant ,Band gap ,Impurity ,Exciton ,Phase (matter) ,Doping ,Fermi energy - Abstract
In this study, we use first-principles calculations to investigate the electronic and structural properties of $\text{Mo}{X}_{2}$ $(X=\text{S}, \mathrm{Se}, \mathrm{Te})$ monolayers doped with substitutional Sb atoms, with a central focus on the Sb(Mo) substitution. In ${\mathrm{MoS}}_{2}$, we observe that this substitution is energetically favored under S-rich conditions, where the ${\mathrm{S}}_{2}$ gaseous phase is likely to be present. This result is compatible with a recent experimental observation in Sb-doped ${\mathrm{MoS}}_{2}$ nanosheets grown by chemical vapor deposition. A similar behavior is found in ${\mathrm{MoSe}}_{2}$, but in ${\mathrm{MoTe}}_{2}$ the Sb(Mo) substitution is less likely to occur due to the possible absence of gaseous Te phases in experimental setups. In all cases, several impurity-induced states are found inside the band gap, with energies that span the entire gap. The Fermi energy is pinned a few tenths of eV above the top of the valence band, suggesting a predominant $p$-type behavior, and gap energies are slightly increased in comparison to the pristine systems. The orbital nature of these states is further investigated with projected and local density of states calculations, which reveal similarities to defect states induced by single Mo vacancies as well as their rehybridization with the $5s$ orbital from Sb. Additionally, we find that the band gap of the doped systems is increased in comparison with the pristine materials, in contrast with a previous calculation in Sb-doped ${\mathrm{MoS}}_{2}$ that predicts a gap reduction with a different assignment of valence band and impurity levels. We discuss the similarities, discrepancies, and the limitations of both calculations. We also speculate possible reasons for the experimentally observed redshifts of the $A$ and $B$ excitons in the presence of the Sb dopants in ${\mathrm{MoS}}_{2}$. We hope that these results spark future investigations on other aspects of the problem, particularly those concerning the effects of disorder and electron-hole interaction, and continue to reveal the potential of doped transition-metal dichalcogenides for applications in optoelectronic devices.
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- 2021
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45. Sublattice dependence and gate-tunability of midgap and resonant states induced by native dopants in Bernal-stacked bilayer graphene
- Author
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François Ducastelle, Eberth A. Quezada-Lopez, Jairo Velasco, C. Bena, Frédéric Joucken, Zhehao Ge, Kenji Watanabe, Takashi Tanagushi, University of California [Santa Cruz] (UCSC), University of California, Arizona State University [Tempe] (ASU), Institut de Physique Théorique - UMR CNRS 3681 (IPHT), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), LEM, UMR 104, CNRS-ONERA, Université Paris-Saclay (Laboratoire d'étude des microstructures), ONERA-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), DMAS, ONERA, Université Paris Saclay [Châtillon], ONERA-Université Paris-Saclay, National Institute for Materials Science (NIMS), J. V. J. acknowledges support from the National Science Foundation under Grant No. DMR-1753367 and the Army Research Office under Contract No. W911NF-17-1-0473. K. W. and T. T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant No. JPMXP0112101001 and JSPS KAKENHI Grant No. JP20H00354., University of California [Santa Cruz] (UC Santa Cruz), University of California (UC), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Materials science ,Band gap ,FOS: Physical sciences ,General Physics and Astronomy ,Tight-binding model ,02 engineering and technology ,Local density of states ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,[SPI]Engineering Sciences [physics] ,Tight binding ,Dopants ,law ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,[CHIM]Chemical Sciences ,010306 general physics ,Scanning tunneling microscopy ,[PHYS]Physics [physics] ,Condensed Matter - Materials Science ,Valence (chemistry) ,Condensed matter physics ,Dopant ,Condensed Matter - Mesoscale and Nanoscale Physics ,Graphene ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,3. Good health ,Scanning tunneling microscope ,0210 nano-technology ,Bilayer graphene - Abstract
The properties of semiconductors can be crucially impacted by midgap states induced by dopants, which can be native or intentionally incorporated in the crystal lattice. For Bernal-stacked bilayer graphene (BLG), which has a tunable bandgap, the existence of midgap states induced by dopants has been conjectured, but never confirmed experimentally. Here, we report scanning tunneling microscopy and spectroscopy results, supported by tight-binding calculations, that demonstrate the existence of midgap states in BLG. We show that the midgap state in BLG -- for which we demonstrate gate-tunability -- appears when the dopant is hosted on the non-dimer sublattice sites. We further evidence the presence of narrow resonances at the onset of the high energy bands (valence or conduction, depending on the dopant type) when the dopants lie on the dimer sublattice sites. These results suggest that dopants/defects can play an important role in the transport and optical properties of multilayer graphene samples, especially at energies close to the band extrema., Includes supplementary material
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- 2021
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46. First-Principles Study on the Stability and Electronic Structure of the Charge-Ordered Phase in α-(BEDT-TTF)2I3
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Hitoshi Seo, Takao Tsumuraya, and Tsuyoshi Miyazaki
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first-principles calculation ,Local density of states ,Materials science ,Crystallography ,Condensed matter physics ,General Chemical Engineering ,Fermi level ,Charge (physics) ,Electronic structure ,Condensed Matter Physics ,electronic structure ,Hybrid functional ,molecular conductor ,Inorganic Chemistry ,Charge ordering ,symbols.namesake ,QD901-999 ,charge ordering ,symbols ,Computer Science::Programming Languages ,General Materials Science ,Density functional theory ,Electronic band structure ,density-functional theory ,hybrid functional - Abstract
We theoretically study the structural and electronic properties of a molecular conductor, α-(BEDT-TTF)2I3, using first-principles density-functional theory calculations, especially in its low-temperature charge-ordered state at ambient pressure. We apply a hybrid functional approach and compare the results with a conventional exchange-correlation functional within the generalized gradient approximation. By performing structural optimization, we found a stable charge-ordered solution for the former, in contrast to the latter approach where the magnitude of the charge imbalance becomes considerably small compared to that when the experimental structure is adopted. The electronic band structure near the Fermi level, with and without structural optimization, as well as the molecule-dependent local density of states of the charge-ordered state are discussed.
- Published
- 2021
47. Electronic properties of atomically coherent square PbSe nanocrystal superlattice resolved by Scanning Tunneling Spectroscopy
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Capiod, Pierre, Van Der Sluijs, Maaike, De Boer, Jeroen, Delerue, Christophe, Swart, Ingmar, Vanmaekelbergh, Daniel, Sub Condensed Matter and Interfaces, Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University [Utrecht], Physique - IEMN (PHYSIQUE - IEMN), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL), European Project: FIRST STEP, Sub Condensed Matter and Interfaces, Condensed Matter and Interfaces, and Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)
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Materials science ,Band gap ,Superlattice ,Scanning tunneling spectroscopy ,Bioengineering ,02 engineering and technology ,semiconductors ,010402 general chemistry ,01 natural sciences ,materials ,law.invention ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,law ,Taverne ,General Materials Science ,Electrical and Electronic Engineering ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Spectroscopy ,Electronic band structure ,Lead selenide ,2D ,Scanning Tunneling Spectroscopy ,Local density of states ,Condensed matter physics ,Mechanical Engineering ,2D, materials ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,nanocrystal superlattices ,scanning tunneling microscopy ,Scanning tunneling microscope ,0210 nano-technology - Abstract
International audience; Rock-salt lead selenide nanocrystals can be used as building blocks for large scale square superlattices via two-dimensional assembly of nanocrystals at a liquid-air interface followed by oriented attachment. Here we report Scanning Tunneling Spectroscopy (STS) measurements of the local density of states of an atomically coherent superlattice with square geometry made from PbSe nanocrystals. Controlled annealing of the sample permits the imaging of a clean structure and to reproducibly probe the band gap and the valence hole and conduction electron states. The measured band gap and peak positions are compared to the results of optical spectroscopy and atomistic tight-binding calculations of the square superlattice band Electronic properties of atomically coherent square PbSe nanocrystal superlattice resolved by Scanning Tunne structure. In spite of the crystalline connections between nanocrystals that induce significant electronic couplings, the electronic structure of the superlattices remains very strongly influenced by the effects of disorder and variability.
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- 2021
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48. Hetero-structure Mode Space Method for Efficient Device Simulations
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Mincheol Shin
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Work (thermodynamics) ,Local density of states ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Nanowire ,FOS: Physical sciences ,General Physics and Astronomy ,Sense (electronics) ,Space (mathematics) ,Condensed Matter - Other Condensed Matter ,symbols.namesake ,Transmission (telecommunications) ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,symbols ,Optoelectronics ,Field-effect transistor ,Hamiltonian (quantum mechanics) ,business ,Other Condensed Matter (cond-mat.other) - Abstract
The Hamiltonian size reduction method or the mode space method applicable to general heterogeneous structures is developed in this work. The effectiveness and accuracy of the method are demonstrated for four example devices, such as GaSb/InAs tunnel field effect transistors (FETs), MoTe 2/SnS 2 bilayer vertical FETs, InAs nanowire FETs with a defect, and Si nanowire FETs with rough surfaces. The Hamiltonian size is reduced to around 5% of the original full-Hamiltonian size without losing the accuracy of the calculated transmission and local density of states in a practical sense. The method developed in this work can be used with any type of Hamiltonian and can be applied virtually to any hetero-structure, and so it has the potential to become an enabling technology for efficient simulations of hetero-structures.
- Published
- 2021
49. Imaging signatures of the local density of states in an electronic cavity
- Author
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Thomas Ihn, Richard Steinacher, Christian Reichl, Beat A. Bräm, Keith R. Fratus, Klaus Ensslin, Andrea Hofmann, Carolin Gold, Werner Wegscheider, Tobias Krähenmann, Michael Sven Ferguson, Dietmar Weinmann, Laboratory for Solid State Physics [ETH Zürich], Department of Physics [ETH Zürich] (D-PHYS), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich)- Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Institute for Theoretical Physics [ETH Zürich] (ITP), Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg (UNISTRA)-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), HQS Quantum Simulations (HQS), and ANR-14-CE36-0007,SGM-Bal,Scanning gate microscopy as a new tool to investigate ballistic transport(2014)
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Work (thermodynamics) ,Local density of states ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,FOS: Physical sciences ,Scanning gate microscopy ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Optoelectronics ,010306 general physics ,0210 nano-technology ,business ,[PHYS.COND.CM-MSQHE]Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall] - Abstract
We use scanning gate microscopy to study electron transport through an open, gate-defined resonator in a Ga(Al)As heterostructure. Raster-scanning the voltage-biased metallic tip above the resonator, we observe distinct conductance modulations as a function of the tip position and voltage. Quantum-mechanical simulations reproduce these conductance modulations and reveal their relation to the partial local density of states in the resonator. Our measurements illustrate the current frontier between possibilities and limitations in imaging the local density of states in buried electron systems using scanning gate microscopy., Physical Review Research, 3 (3), ISSN:2643-1564
- Published
- 2021
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50. Solving the electronic structure problem with machine learning
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Anand Chandrasekaran, Lihua Chen, Rohit Batra, Rampi Ramprasad, Deepak Kamal, and Chiho Kim
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lcsh:Computer software ,Emulation ,Local density of states ,Artificial neural network ,Computer science ,business.industry ,Function (mathematics) ,Machine learning ,computer.software_genre ,Computer Science Applications ,lcsh:QA76.75-76.765 ,Mechanics of Materials ,Modeling and Simulation ,Component (UML) ,Physics::Atomic and Molecular Clusters ,lcsh:TA401-492 ,General Materials Science ,Density functional theory ,lcsh:Materials of engineering and construction. Mechanics of materials ,Artificial intelligence ,Invariant (mathematics) ,Representation (mathematics) ,business ,computer - Abstract
Simulations based on solving the Kohn-Sham (KS) equation of density functional theory (DFT) have become a vital component of modern materials and chemical sciences research and development portfolios. Despite its versatility, routine DFT calculations are usually limited to a few hundred atoms due to the computational bottleneck posed by the KS equation. Here we introduce a machine-learning-based scheme to efficiently assimilate the function of the KS equation, and by-pass it to directly, rapidly, and accurately predict the electronic structure of a material or a molecule, given just its atomic configuration. A new rotationally invariant representation is utilized to map the atomic environment around a grid-point to the electron density and local density of states at that grid-point. This mapping is learned using a neural network trained on previously generated reference DFT results at millions of grid-points. The proposed paradigm allows for the high-fidelity emulation of KS DFT, but orders of magnitude faster than the direct solution. Moreover, the machine learning prediction scheme is strictly linear-scaling with system size.
- Published
- 2019
- Full Text
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