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We manipulated the stacking configuration of a few-layer MoS2 to investigate the impact of interlayer coupling on electrical band engineering. By simultaneously synthesizing two distinct stacking types of MoS2 islands, wedding cake (W) and spiral (S), on the same substrate, we explored layer-dependent electrical properties under identical experimental conditions. We used multiple scanning probe microscopy techniques to map local electronic properties with respect to the number of layers, stacking configurations, and local heterogeneities. First-principles calculations verified the role of distinct interlayer coupling in terms of the interlayer distance. Our findings highlight the critical role of interlayer coupling in applications of transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Structural stability, local density of states, bonding information, and charge distribution differences of C‐substituted ZnO (C/VZnxOy) monolayer structures, as well as their interactions with lithium atoms, are investigated using the density functional theory (DFT) method. The energy required to generate vacancies in pristine ZnO monolayers is considerably high, but since the C atoms are strongly adsorbed in the vacant sites, the energy required to form C/VZnxOy structures is reduced. These lattice substitutions cause an alteration of the Zn d‐states. The bonding analysis shows that the C−O interaction is stronger than the C−Zn interaction. So, it generates high stability for these structures. Furthermore, because the development of C/VZnxOy is aimed at lithium battery electrode applications, the most fundamental thing that needs to be examined initially is the interaction between the C/VZnxOy surfaces and the lithium atoms. Li3 strongly binds on all C/VZnxOy surfaces, and it turns to Li3+ based on a simple analysis of charge distribution differences. These findings will have a substantial impact on the future development of ZnO monolayers, and their potential as lithium battery electrodes can be studied further. [ABSTRACT FROM AUTHOR]

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]

Flat band has attracted more and more interest in recent years, motivated by its discovery in twisted bilayer graphene (TBG). In this work, we report our study of the impurity effect on this flat band system, which is an important issue for real materials. Employing the Lanczos recursive method, we solve the local density of states (LDOS) around a potential impurity. We find for large impurity size, a series of bound states are formed inside the impurity, and the flat band peak in LDOS is suppressed near the impurity boundary and shifted by the impurity potential deep inside the impurity. As the impurity size becomes smaller, the effect on the flat band becomes weaker, as anticipated from the large scale of the underlying Wannier function. This property distinguishes with the usual flat band systems with small localized Wannier orbitals, and indicates the flat band in TBG is more stable against small-size impurities. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots display remarkable optical and electrical characteristics with the potential for extensive applications in contemporary nanotechnology. As an ideal instrument for examining surface topography and local density of states (LDOS) at an atomic scale, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has become indispensable approaches to gain better understanding of their physical properties. This article presents a comprehensive review of the research advancements in measuring the electronic orbits and corresponding energy levels of colloidal quantum dots in various systems using STM and STS. The first three sections introduce the basic principles of colloidal quantum dots synthesis and the fundamental methodology of STM research on quantum dots. The fourth section explores the latest progress in the application of STM for colloidal quantum dot studies. Finally, a summary and prospective is presented. [ABSTRACT FROM AUTHOR]

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.

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.

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.

Anisotropic gold nanoparticles (AuNPs) were synthesized using microwave (MW)-assisted route. Lemon extract was used as both reducing and stabilizing agent. Subsequent UV treatment was carried out to modify the particle size and shape. Distribution of triangular and pentagonal-shaped particles were found to increase in number. Moreover, up to 60% increase in particle size was also observed. Change in optical property and appearance of plasmon modes were clear indication of the modification caused. Local density of photonic states (LDOS) and electric field distribution were obtained through computational simulation using MATLAB toolbox. Experimental results were used as the input values for the simulation. Dipolar distribution was observed along the boundaries of the spherical NPs, while for triangular and pentagonal-shaped NPs, they were found to be concentrated along their edges and corners. The results presented here encourage us to choose an alternative eco-friendly, quick and simple route to synthesize gold NPs of various shapes for various application such as in viral detection, nanobiomaterials, biomedical images, detection-therapy, etc. New, rapid, and eco-friendly route to synthesize anisotropic gold nanoparticles (AuNPs) using microwave-assisted method is proposed. Subsequent UV treatment of the synthesized AuNPs did modify their size and shape. An increase in their size of up to 60% was recorded along with the change in their shape from spheroidal to triangular, pyramidal, and pentagonal. Plasmonic peaks obtained experimentally were used in theoretical study to understand the distribution of electrical fields. Using simulated results, the dominant geometric contributions of the plasmon resonances were mapped. [ABSTRACT FROM AUTHOR]

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]

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.

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.

The optical Raman cooling implies enhanced anti-Stokes scattering compared to Stokes scattering. Plasmon-enhanced Raman scattering in a layered insulator-metal-insulator (IMI) system occurs due to the modification of the local density of electromagnetic states (LDOS) near a metallic layer. Because both eigenmodes with frequencies below the plasma frequency are surface modes and the high-frequency mode is delocalized, energy is capable of dissipating into free space through anti-Stokes scattering. In this work, we carry out the numerical simulation of LDOS for IMI structures with a varied thickness of the metallic layer. Our work is a step towards the development of structured photonic materials for optical cooling of solids. [ABSTRACT FROM AUTHOR]

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.

In this paper, we first characterize a superlattice structure created by repeating a heterostructure formed from two armchair graphene nanoribbon (AGNR) segments with different widths. We investigate the electronic and transport properties of this structure by varying its widths and lengths to demonstrate the tunability of its overall band gap. The plot of the local density of states shows the formation of localized states at the low band gap segments of the superlattice. The superlattice is then used as a barrier to create a double barrier quantum well (DBQW) to design a proposed resonant tunneling diode (RTD) structure. We observe this device's negative differential resistance (NDR) operation for a range of bias voltages between the contacts. We study the effect of dimensional parameters on the RTD performance. The non-equilibrium Green's function method, based on a tight-binding model, is employed for numerical computation. • Tight binding approach considering overlapping matrix and hopping parameter up to 3rd nearest neighbor. • Band gap modulation of U-cut edge patterned AGNR. • Transport properties of DBQWs for graphene nanoribbon using Non equilibrium green's function. • LDOS at the quasi bound state due to quantum well. • Performance of graphene based Resonant Tunneling Diode. [ABSTRACT FROM AUTHOR]

This paper aims to elucidate the effect of an air‐formed native oxide covering mild steel surface on the contrast in the scanning electron microscopy (SEM) images obtained with the landing energy from 5 keV down to 0 eV. Part of the mild steel surface was in‐situ cleaned by Ar+ ion sputtering process in order to remove native oxide from the surface. It enabled us to observe the oxide‐free and the naturally oxidized area on the mild steel surface simultaneously in the SEM micrographs. Presence of the native oxide starts to play a role in the SEM images acquired at landing energy below roughly 3 keV. Contrast between differently oriented grains situated inside the area covered by the native oxide starts to be negligible with landing energy decreasing below 3 keV, up to some ultra‐low values where the contrast increases again. Total reflectivity contrast between the clean and the oxidized area increases exponentially with landing energy decreasing below 3 keV. The reflectivity‐versus‐energy curves of the cleaned and the naturally oxidized mild steel surface are markedly different. The reflectivity of the electrons is correlated with the density of states (DOS), as is demonstrated at very low landing energies. Sensitivity of the very low‐energy electrons to the electronic structure was verified by comparison of the experimental data with the simulations of reflectivities, band structure, and DOS. The theoretical predictions are based on the density‐functional theory calculations and they have been performed in energy range corresponding to specular reflectivities of the Fe‐BCC (001) orientation. We have also observed that close to the mirror condition, that is, near‐zero landing energies, the primary electrons become sensitive to the surface potential differences caused by the work function differences of clean and native oxide‐covered steel surfaces. [ABSTRACT FROM AUTHOR]

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 N2 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]

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]

In this article we consider asymptotics for the spectral function of Schrödinger operators on the real line. Let PWL2(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]

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.

SnSe, an environmental-friendly group-IV monochalcogenide semiconductor, demonstrates outstanding performance in various applications ranging from thermoelectric devices to solar energy harvesting. Its ultrathin films show promise in the fabrication of ferroelectric nonvolatile devices. However, the microscopic identification and manipulation of point defects in ultrathin SnSe single crystalline films, which significantly impact their electronic structure, have been inadequately studied. This study presents a comprehensive investigation of point defects in monolayer SnSe films grown via molecular beam epitaxy. By combining scanning tunneling microscopy (STM) characterization with first-principles calculations, we identified four types of atomic/molecular vacancies, four types of atomic substitutions, and three types of extrinsic defects. Notably, we have demonstrated the ability to convert a substitutional defect into a vacancy and to reposition an adsorbate by manipulating a single atom or molecule using an STM tip. We have also analyzed the local atomic displacement induced by the vacancies. This work provides a solid foundation for engineering the electronic structure of future SnSe-based nanodevices.

• 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]

• A gradient-free topological optimization framework to customize desired Dirac-like cones and extended problems. • Some novel photonic crystals with unprecedented performance are designed. • Pseudo-spin topological insulators with ultra-wide overlapping bandgap (26.95%) are designed. • Various wave manipulation capabilities of optimized photonic crystals are demonstrated. As the cornerstone of various exotic optical properties, the Dirac-like cones (DCs) in photonic crystals (PhCs) have attracted ever-increasing attention. Based on the concept of local density of states (LDOS) and the method of material-field series expansion (MFSE), this study proposes a general topology optimization framework to systematically realize the inverse design of customizing DCs considering different frequencies, structural symmetries, degeneracies, and even degenerate modes. According to the proposed framework, we further develop some novel PhCs with unprecedented performance, such as the PhCs with dual-polarization DCs that combine good manufacturability and high accuracy of degeneracy, frequency-separated dual-DCs for single/dual polarization in nonlinear optical, semi-Dirac cones with strict and special dispersion relationship for asymmetric transmission, and a pair of pseudo-spin topological insulators with ultra-wide overlapping band gap (26.95%). Full-wave numerical simulations validate various wave manipulation capabilities of optimized PhCs, such as cloaking effect, electromagnetic tunneling, asymmetric transport, unidirectional and topologically protected transport. This work contributes towards the development of complex multi-functional PhCs with desired DCs, and provides an effective and robust inverse design toolbox for topological optics. [ABSTRACT FROM AUTHOR]

Recently a novel surface pair-density-wave (PDW) superconducting state has been discovered in Barkman et al. (2019) and Samoilenka et al. (2020), which may go through a distinct multiple phase transition (MPT) when the superconductivity fades away from bulk to the boundary (e.g. edges and corners). Based on the Bogoliubov-de Gennes equations for the attractive tight-binding Hubbard modal in a one-dimensional chain, we demonstrate that the surface PDW state has a non-gapless quasiparticle spectrum, which is contrary to the conventional surface superconducting state. Moreover, we find that the MPT is associated with a zero-bias fast oscillating pattern in the LDOS near the surface. Our findings provide a potential experimental clue to identify the surface PDW state. • The energy spectra of surface PDW superconducting states are non-gapless. • The associated multiple phase transition shows zero-bias fast oscillating LDOS. • The surface DOS increases with the bias at temperature below the surface T cs. [ABSTRACT FROM AUTHOR]

The electronic properties of the surface of β -FeSi 2 have been debated for a long. We studied the surface states of β -FeSi 2 films grown on Si(001) substrates using scanning tunnelling microscopy (STM) and spectroscopy (STS), with the aid of density functional theory calculations. STM simulations using the surface model proposed by Romanyuk et al (2014 Phys. Rev. B 90 155305) reproduce the detailed features of experimental STM images. The result of STS showed metallic surface states in accordance with theoretical predictions. The Fermi level was pinned by a surface state that appeared in the bulk band gap of the β -FeSi 2 film, irrespective of the polarity of the substrate. We also observed negative differential conductance at ∼0.45 eV above the Fermi level in STS measurements performed at 4.5 K, reflecting the presence of an energy gap in the unoccupied surface states of β -FeSi 2 ., (© 2023 IOP Publishing Ltd.)

Mismatch between adjacent atomic layers in low-dimensional materials, generating moiré patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear as ideal candidates for the study of these phenomena due to the weak coupling between layers. Here we discover and investigate the origin of 1D moiré stripes on the surface of Bi 2 Se 3 TI thin films and nanobelts. Scanning tunneling microscopy and high-resolution transmission electron microscopy reveal a unidirectional strained top layer, in the range 14-25%, with respect to the relaxed bulk structure, which cannot be ascribed to the mismatch with the substrate lattice but rather to strain induced by a specific growth mechanism. The 1D stripes are characterized by a spatial modulation of the local density of states, which is strongly enhanced compared to the bulk system. Density functional theory calculations confirm the experimental findings, showing that the TI surface Dirac cone is preserved in the 1D moiré stripes, as expected from the topology, though with a heavily renormalized Fermi velocity that also changes between the top and valley of the stripes. The strongly enhanced density of surface states in the TI 1D moiré superstructure can be instrumental in promoting strong correlations in the topological surface states, which can be responsible for surface magnetism and topological superconductivity.

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 SiO 2 , 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. • The Green function is used studying the effects of pressure on the local density states. • The band structure shows a shift at high frequencies with pressure. • Existence of a defective mode inside PBG. [ABSTRACT FROM AUTHOR]

• Vortices respond to the anisotropies of the gap and Fermi surface in different ways. • Straight flow trajectories of quasiparticles with splitting induced by an anisotropic Fermi surface. • Curved flow trajectories of quasiparticles and intensity reversals induced by an anisotropic gap. A theoretical study on the vortex image is carried out near a vortex core in the presence of the anisotropic superconducting gap or the anisotropic Fermi surface with fourfold symmetry by solving Bogoliubov-de Gennes (BdG) equations. Both results show the anisotropic vortex core with fourfold symmetry, but detailed structures are rather different. At zero energy, the local density of states (LDOS) is always larger along curvature minima than along curvature maxima of the Fermi surface at the same radial distances from the vortex center in the presence of the anisotropic Fermi surface. In contrast, in the presence of the anisotropic superconducting gap, the LDOS is larger along gap maxima than along gap minima at short distances, but with an inversion at larger distances. With increasing energy, the evolutions of vortex images in these two situations also behave quite differently. Our results provide an effective method to distinguish these two contributions from the anisotropic superconducting gap and Fermi surface to the vortex image. [ABSTRACT FROM AUTHOR]