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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.

International audience; We investigate the existence of Tamm states at the interface between two one-dimensional (1D) photonic crystals (PCs) through an analysis of local density of states (LDOS) using the Green’s function method. The PCs are made of a comb-like structure consisting of stubs grafted periodically along a waveguide with different geometrical parameters. The Tamm states appear as maxima in the LDOS inside the common bandgaps of the periodic PCs. In addition, we prove the existence of such Tamm states using a topological invariant based on the Zak phase of the bulk band for each PC. The Zak phase is calculated using two different arguments, namely (i) the symmetry of the electric field at the band edge states and (ii) the sign of the reflection phases between each PC and a given waveguide. The Tamm state appears as well-defined resonance in the bandgap frequency area of the transmission spectra through two finite PCs in tandem. Our proposed design can be used as filter and sensor.

In this work, we have investigated the structural and electronic properties of Mg-doped GaAs(111) nanowires synthesized through a vapor–liquid–solid growth mechanism. The crystalline structure of t...

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.

Craters have been observed upon irradiation by single ion impacts of Ar monomer and Ar dimer ions with 35 keV/atom in monolayer graphene on copper at a fluence of 1 × 1012 atoms/cm2. The observed craters at the ion impacts are in the underlying copper substrate, which pull down the graphene layer conformally towards them, introducing disorder into graphene. The number density of craters per atom produced by Ar-monomers is higher than that of Ar-dimer ions. In the ion impact region, disorder is high, and graphene is metallic in both Ar-monomer and dimer irradiation. In the ion impact region of dimer irradiated graphene, local density of states is higher and there is a shift in Dirac point position by +0.07 eV and a bandgap opening of 0.25 eV in the ordered region ∼15 nm away from the ion impact. Microscopic ripples in graphene are not observed in the case of monomer irradiation while they are present in the case of dimer irradiation with a reduced wavelength. Isotropic compressive strain is introduced by the ion impacts and it is larger for Ar-dimer irradiation. The combined effects of compressive strain along with breaking the equivalence between A and B sublattice of graphene is attributed to the opening of the band gap in graphene.

The structure and edge states of two-dimensional few-layer Bi(110) films grown on a graphene/SiC substrate were studied by low-temperature scanning tunneling microscopy and spectroscopy. We found that the local density of states of few-layer Bi(110) films are layer-dependent and that the films transition from exhibiting semiconducting characteristics to metallic ones as the number of layers increases. The in-plane lattice structure has numerous displacements and inversions, which implies that the atomic arrangement and atomic buckling in ultrathin Bi(110) films are flexible. The edges formed between 4-monolayer Bi(110) and graphene are reconstructed and distorted, and the corresponding edge states are topographically dependent. Steps from the substrate and domain boundaries also modify the electronic structures and induce additional defect-dependent states, We also found that the zigzag-shaped step edges in few-layer Bi(110) films are nonreconstructed and possess layer-dependent homogeneous edge states, providing a very likely platform for further research on quantum interference of the edge mode in order to confirm the topology in Bi(110).

In this work, theoretical investigation in coherent manipulation throughout local density of states calculation for serially coupled double quantum dots embedded between ferromagnetic leads (FM-QD1-QD2-FM) by using the non-equilibrium Green's function approach. Since the local density of states are formulated incorporating the spin polarization and the type of spin configuration on the leads. Our model incorporates the inter-dot hopping, the intra-dot Coulomb correlation, the spin exchange energy and the coupling interactions between the quantum dots and leads. The results concerned to the parallel configuration at strong inter-dot coupling regime shows that the spin down electrons in the quantum dots may be more coupled coherently if the regime is tuned. The local density of states of the two dots for spin up electrons shows a broad hump with small splitting i.e. the case is decoherent for spin up electrons. In the case of weak interdot coupling it is obvious that the spin dependent density of states on the quantum dots show that the resonances are not well splitted. For the antiparallel configuration in the strong coupling regime, the spin dependent density of states of the double quantum dots show four peaks but with broaden and overlapping. In the case of weak coupling regime, the total spin dependent density of states, which have two peaks with certain board, one can conclude that the states are not coupled coherently. The case of the antiferromagnetic nature of the spin exchange interaction, our calculations for the parallel and antiparallel configurations (in strong and weak regimes) show a decoherence state.

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.

The vortex states in electron-doped high-Tc superconductors are studied theoretically at the mean-field approach and based on the Bogoliubov-de Gennes equations. The local density of states is calculated, through which the in-gap bound states are revealed. They are robust at the sites around the vortex core. In the underdoped region where the antiferromagnetic order and the superconducting order coexist, the in-gap peaks are lying symmetric with respect to the Fermi energy, while the peak intensities at the negative energy are much stronger. A stripe-type modulation is revealed for the spin-resolved local density of states. As the doping density increases to the optimal or over-doped region, the long-range antiferromagnetic order disappears, and the two in-gap peaks merge to one single peak. The peak position is near the Fermi energy. Our results indicate that the vortex states may be used to detect the signature of the antiferromagnetic order in electron-doped high-Tc superconductors.

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.

We examine the transport properties of multi-channels of a porphyrin phenylacetylene (PPA) molecule by changing gate and source voltages at its two terminals. Density functional theory (DFT) within the non-equilibrium Green's function framework (NEGF) is employed to calculate the four probe PPA device by connecting with four Au electrodes using S linkages. Two gate voltages are chosen as 0.6 V (denoted as PPA-0.6) and 1.0 V (denoted as PPA-1.0), respectively. At each certain gate voltage, source voltages are applied in the range of 0.0 V to 1.0 V at a step of 0.2 V. It is found that the magnitude of the gate voltage plays a significant role in the whole transport property. No matter in PPA-0.6 or in PPA-1.0, evident NDR behavior is observed for lead currents. Moreover, a smaller gate voltage could induce a more prominent NDR effect. On the other hand, the relative magnitude of the gate voltage and the source voltage determines the current directions of the gate and source leads. Furthermore, input/output current switches can be achieved for the gate lead at the critical voltage of Vgate = Vsource. These interesting transport characteristics are further analyzed from the transmission spectra and the local density of states (LDOS). This presentation provides a clue for exploring novel functional nano-electronic molecular devices based on PPA by tuning gate voltages and source voltages as well as changing lead-to-lead channels.

Density functional theory method was used to study the interaction of 3d-transition metal ions with divacancy in graphene. Calculations demonstrate that in all cases, except for that of the structure with the Sc ion, the metal is located in the divacancy center, compensating for the four dangling chemical bonds of carbon atoms. Interaction energies are close to 1000 kJ/mol. The strongest interaction was found for the Ni ion. Analysis of the local density of states of nanoparticles shows that additional energy levels appear in the energy gap between the highest occupied and lowest unoccupied levels of the graphene cluster due to the presence of a transition metal ion. In the case of clusters with Co, Ti, and V ions, the highest occupied level of the cluster lies in the region of electronic states with non-zero local density on the ion.

Using density functional theory (DFT) calculations, we examined the effects of substitutional doping on the formation of Cu vacancies in Cu2O(111). Upon replacing coordinatively unsaturated O with other elements (N, F, P, S, and Cl) and calculating the formation energies, we found that compared to the undoped surface, Cu vacancy formation is most favorable in the F-doped surface and least favorable in the N-doped Cu2O(111) surface. In addition, we found that in most cases, vacancy formation of the coordinatively saturated Cu has higher vacancy formation energy than coordinatively unsaturated Cu atoms. In the electron localization function plots and the projected charge distributions of the local density of states, we found bonding enhancement between Cu and N in N-Cu2O(111) but no corresponding enhancement was observed in the F-doped surface. Our results showed that the interaction between the substitutional dopants and the Cu atoms affects the formation of the doped system and the Cu vacancy formation in the surface.

Layered metal-dielectric structures are easy-to-fabricate one-dimensional plasmonic metamaterials. Using the effective media approach, we consider surface plasmons that appear on an interface between such metamaterial and a dielectric. We have shown that two types of surface plasmon states appear on an interface. The frequency of the peak in the local density of states of these states is dependent on the fraction of metal in the metamaterial. By reducing the fraction, the frequency can be shifted towards longer wavelengths. There the losses of light in metal are reduced, which, as we have shown, leads to the increase in peak value of the Purcell factor.

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.

A novel family of disordered systems is proposed. This family belongs to the class of systems containing random substitutional non-Hermitian impurities. We limit our consideration to a rather simple case when the presence of substitutional point defects results in the model Hamiltonian featuring a diagonal disorder. In contrast to known models of non-Hermitian impurities, the nonzero density of states for each isolated from the host impurity is restricted to a continuous band of finite width. A method to construct corresponding impurity Hamiltonians is provided.

Using scanning tunneling microscopy/spectroscopy (STM/STS), we examine quasiparticle scattering and interference properties at the surface of WTe2. WTe2, layered transition metal dichalcogenide, is predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 emerge as topologically protected touching points of electron and hole pockets, and Fermi arcs connecting them can be visible in the spectral function on the surface. To probe the properties of surface states, we have conducted low-temperature STM/STS (at 2.7 K) on the surfaces of WTe2 single crystals. We visualize the surface states of WTe2 with atomic scale resolution. Clear surface states emerging from the bulk electron pocket have been identified and their connection with the bulk electronic states shows good agreement with calculations. We show the interesting double resonance peaks in the local density of states appearing at localized impurities. The low-energy resonant peak occurs near the Weyl point above the Fermi energy and it may be mixed with the surface state of Weyl points, which makes it difficult to observe the topological nature of the Weyl semimetal WTe2.

Cathodoluminescence can probe photonic responses of nanostructures at high spatial and energy resolution, providing a powerful tool to investigate the radiative properties under electron excitation...

Graphene nanoribbons (GNRs) attract a growing interest due to their tunable physical properties and promise for device applications. A variety of atomically precise GNRs have recently been synthesized by on-surface and solution approaches. While on-surface GNRs can be conveniently visualized by scanning tunneling microscopy (STM), and their electronic structure can be probed by scanning tunneling spectroscopy (STS), such characterization remains a great challenge for the solution-synthesized GNRs. Here, we report solution synthesis and detailed STM/STS characterization of atomically precise GNRs with a meandering shape that are structurally related to chevron GNRs but have a reduced energy band gap. The ribbons were synthesized by Ni0-mediated Yamamoto polymerization of specially designed molecular precursors using triflates as the leaving groups and oxidative cyclodehydrogenation of the resulting polymers using Scholl reaction. The ribbons were deposited onto III-V semiconducting InAs(110) substrates by a dry contact transfer technique. High-resolution STM/STS characterization not only confirmed the GNR geometry, but also revealed details of electronic structure including energy states, electronic band gap, as well as the spatial distribution of the local density of states. The experimental STS band gap of GNRs is about 2 eV, which is very close to 2.35 eV predicted by the density functional theory simulations with GW correction, indicating a weak screening effect of InAs(110) substrate. Furthermore, several aspects of GNR-InAs(110) substrate interactions were also probed and analyzed, including GNR tunable transparency, alignment to the substrate, and manipulations of GNR position by the STM tip. The weak interaction between the GNRs and the InAs(110) surface makes InAs(110) an ideal substrate for investigating the intrinsic properties of GNRs. Because of the reduced energy band gap of these ribbons, the GNR thin films exhibit appreciably high electrical conductivity and on/off ratios of about 10 in field-effect transistor measurements, suggesting their promise for device applications.

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.

Electronic interface properties and the initial growth of hexa-peri-hexabenzocoronene with a borazine core (BN-HBC) on Au(111) have been studied by using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A weak, but non-negligible, interaction between BN-HBC and Au(111) was found at the interface. Both hexa-peri-hexabenzocoronene (HBC) and BN-HBC molecules form well-defined monolayers. The different contrast in STM images of HBC and BN-HBC at different tunneling voltages with submolecular resolution can be ascribed to differences in the local density of states (LDOS). At positive and negative tunneling voltages, STM images reproduce the distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as determined by density functional theory (DFT) calculations very well.

The electronic spectrum of graphene with a single point impurity is considered. Local densities of states at the impurity site and its nearest neighbors are calculated analytically. Their evolution...

The total electron densities of states for graphene nanoribbons with edges of different chirality, as well as the electron local densities of states for individual atoms in these nanoribbons, are calculated and analyzed. There are sharp resonance peaks near the Fermi level in the total electron densities of states of graphene nanoribbons with zigzag edges, which emerge only in the local densities of atoms from the sublattice that goes directly to the nearest edge (i.e., whose atoms have dangling bonds). Semiconducting gaps appear in the spectra of graphene nanobands with armchair chirality edges having a number of constituent atomic lines that is either a multiple of three, or gives a remainder of one when divided by three. The width of this gap only depends on the width of the nanoribbon, and is the same for all its atoms. The electron spectra of graphene nanoribbons with armchair-chirality edges have a metallic behavior if the number of atomic lines gives a remainder of two when divided by three. However, semiconducting gaps still manifest on the local densities of the atoms belonging to some lines of such nanoribbons.The total electron densities of states for graphene nanoribbons with edges of different chirality, as well as the electron local densities of states for individual atoms in these nanoribbons, are calculated and analyzed. There are sharp resonance peaks near the Fermi level in the total electron densities of states of graphene nanoribbons with zigzag edges, which emerge only in the local densities of atoms from the sublattice that goes directly to the nearest edge (i.e., whose atoms have dangling bonds). Semiconducting gaps appear in the spectra of graphene nanobands with armchair chirality edges having a number of constituent atomic lines that is either a multiple of three, or gives a remainder of one when divided by three. The width of this gap only depends on the width of the nanoribbon, and is the same for all its atoms. The electron spectra of graphene nanoribbons with armchair-chirality edges have a metallic behavior if the number of atomic lines gives a remainder of two when divided by three. Howeve...

Covalent organic frameworks (COFs) are molecule-based 2D and 3D materials that possess a wide range of mechanical and electronic properties. We have performed a joint experimental and theoretical study of the electronic structure of boroxine-linked COFs grown under ultrahigh vacuum conditions and characterized using scanning tunneling spectroscopy on Au(111) and hBN/Cu(111) substrates. Our results show that a single hBN layer electronically decouples the COF from the metallic substrate, thus suppressing substrate-induced broadening and revealing new features in the COF electronic local density of states (LDOS). The resulting sharpening of LDOS features allows us to experimentally determine the COF band gap, bandwidths, and the electronic hopping amplitude between adjacent COF bridge sites. These experimental parameters are consistent with the results of first-principles theoretical predictions.

The tritium release behavior of the Li2TiO3 crystal has become an important index to evaluate its comprehensive performance as a solid breeder material in nuclear fusion reactors. The tritium diffusion on the surface (surface diffusion) and diffusion from the inside to the surface (hopping diffusion) in Li2TiO3 crystals with a 1/3-Li(001) surface are systematically investigated by the first-principles method. Possible adsorption sites, diffusion pathways and energy barriers of surface diffusion and hopping diffusion have been calculated and analyzed, respectively. Tritium atoms are found to diffuse preferentially along the [100] direction on the surface and two equivalent pathways across the surface were identified. The obtained activation energies are about 0.50 eV for surface diffusion and 1.56 eV for hopping diffusion. The local density of states and Bader charge for typical surface diffusion and hopping diffusion pathways are calculated and analyzed. The results reveal that the tritium (T) atom bonds with neighboring oxygen (O) atoms during the surface diffusion, while the T–O interaction is significantly weakened in the hopping diffusion which results in the higher activation energy than that of surface diffusion. In combination with our previous work, a complete tritium diffusion model for the Li2TiO3 crystal is proposed and the corresponding tritium diffusion coefficients are obtained. Our obtained activation energies are in the same range as previous experimental data and could provide theoretical support for the future related experiments.

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.

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

This work presents an investigation of carrier transport in $\mathrm{Ga}\mathrm{N}$-based light-emitting diodes in the subthreshold forward-bias regime where tunneling processes are relevant. A quantum kinetic theory of trap-assisted tunneling is developed within the framework of the nonequilibrium Green's function formalism. Based on fully nonlocal scattering self-energies computed in the self-consistent Born approximation and a multiband description of the electronic structure, the model provides access to spectral quantities, such as the local density of states and the current density, which are essential to understand the nature of the tunneling process. The quantum nonradiative recombination rates can be reproduced by the conventional Shockley-Read-Hall theory, provided that the classical charge is replaced with the correct quantum charge, which means that trap-assisted tunneling can be described with drift-diffusion solvers complemented with appropriate quantum corrections for the calculation of the local density of states. The subthreshold $I$-$V$ characteristics and ideality factors predicted by the quantum kinetic model are in agreement with measurements.

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.

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.

In this talk I show how to find materials supporting topological edge states through extending the concept of the refractive index. Rather than compute a topological invariant, we compute the refractive index as a function of propagation direction, finding that zero index in a complex direction corresponds to one-way propagation. As well as providing an alternative viewpoint, we find a circulation dependent local density of states, an optical instance of the Atiyah–Singer index theorem, and a re-interpretation of spin–momentum locking.

The interaction between light and plasmonic structures at the deep-nanometer scale, which is essentially governed by nonclassical effects, has been increasingly investigated by the hydrodynamic model. Several hydrodynamic models have been introduced, in order to describe the motion of the free electron gas in metals. In this work, by employing the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM), the nonlocal response of an isolated metallic nanoparticle, excited by a dipole emitter, is investigated. The analysis is performed for the local density of states of an emitter coupled with a spherical nanoparticle, which may be treated analytically. Both radial and tangential emitters are studied, while varying the emitter–nanoparticle separation, and the nanoparticle’s size and material. It is shown that HW-HDM and Q-HDM may generate striking spectral features, which do not arise within the classical approach.

Spontaneous light emission is known to be affected by the local density of states and enhanced when coupled to a resonant cavity. Here, we report on an experimental study of silicon-vacancy (SiV) color center fluorescence and spontaneous Raman scattering from subwavelength diamond particles supporting low-order Mie resonances in the visible range. For the first time to our knowledge, we have measured the size dependences of the SiV fluorescence emission rate and the Raman scattering intensity from individual diamond particles in the range from 200 to 450 nm. The obtained dependences reveal a sequence of peaks, which we explicitly associate with specific multipole resonances. The results are in agreement with our theoretical analysis and highlight the potential of intrinsic optical resonances for developing nanodiamond-based lasers and single-photon sources.

In the framework of the microscopic Bogoliubov–de Gennes theory, we investigate the vortex and skyrmionic states as well as phase transitions between them in mesoscopic superconducting squares with coexisted spin-triplet (p-wave) and spin-singlet (s-wave and d-wave) pairing symmetries. By choosing different chemical potential $$\mu $$ , the influence of next-nearest-neighbor hopping $$t'$$ on the evolution of mixed pairing orders is mainly discussed. For the case of small $$|\mu |$$ in which the triplet $$p_{x}\pm {i}p_{y}$$ -wave symmetry is dominant, the skyrmionic structures containing the vortex-antivortex pair become stable at appropriate external magnetic flux. The transitions between different coreless skyrmionic modes can take place with tuning $$t'$$ . For further enlarged $$|\mu |$$ , the singlet s-wave component is gradually enhanced in the present mescoscopic sample. We can obtain the transitions between different multivortex states and between the multivortex and skyrmionic states when $$t'$$ is varied. The corresponding zero-energy local density of states and the relative phase differences are provided to display different topological defects.

Local phenomena of materials generate strongly localized electromagnetic wave, called thermally excited evanescent waves, in the long-wavelength infrared spectra range. In order to directly detect the spectroscopic information of the thermally excited evanescent wave, we have developed passive near-field optical spectroscopy (SNOS) based on grating-based spectroscopy. Using the passive SNOS, we achieved detecting the thermally excited evanescent waves on an Au/SiC micropattern sample at different wavelengths. The detected near-field signals were well consistent with the electromagnetic local density of states of SiC and Au. Passive SNOS will be a powerful tool for numerous spectroscopic applications including a surface chemical analysis.

Using the tight-binding approach, we investigate the electronic and magneto-optical properties of bilayer phosphorene quantum dots (BLPQDs) in the presence of perpendicular electric and magnetic fields. The magneto-energy spectra of the BLPQDs exhibit Aharonov–Bohm oscillations. The period and the amplitude of the oscillation decrease with the size of the BLPQDs. An oscillatory behavior of the local density of states (LDOS) versus the magnetic field is observed, as well as the appearance of the spatial Aharonov–Bohm oscillations in the LDOS. In the absence of the electric field, there exists an s-fold degeneracy (s absolutely flat bands at exactly zero energy) arising from the edge-mode states, where s is the smaller value between M and N, where M and N are the number of phosphorus atoms along the x and y axis, respectively, in a rectangular BLBPQD. The absorption spectra of the BLPQDs are obtained for both in-plane and out-of-plane polarizations. Compared with the absorption spectra of graphene dots, the absorption of an out-of-plane polarization of the incident light is high compared to that of in-plane polarizations. On the other hand, the absorption spectra due to in-plane polarizations are almost the same in the case of graphene, whereas they are considerably different in BLBPQDs. Importantly, the appearance of several sharp and high absorption peaks in the near-infrared (NIR) range dictates the BLBPQDs for application and development of bioimaging, biomedicine and drug delivery technology. More importantly, both the location and intensity of these NIR peaks depend characteristically on the orientation of the polarization of the incident light, which can be desirably tuned by the simultaneous engineering of magnetic and electric fields. Such unique advantage of the anisotropic optical feature enables a new degree of freedom for achieving novel polarization-dependent photonic devices. The dual magnetic and electric field tunable optical and electrical features of the BLPQDs are expected to have important consequences for the development of multifunctional magneto-optoelectronic devices and provide insight into the applicability of quantum photopic technologies based on BLBPQDs.

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes. Graphitized domains of a few nanometers are shown to manifest the effects of boron dopants on the BDD surface. Confirmed by first-principles calculations, local density of states measurements reveal that the electronic structure of these features is characterized by in-gap states induced by boron-related lattice deformation. The dopant-related graphitization is uniquely observed in BDD (111), which explains its electrochemical superiority over the (100) facet. These experimental observations provide atomic-scale information about the role of dopants in modulating the conductivity of diamond, as well as, possibly, other functional doped materials.

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

Shubnikov-de Haas oscillations are the most well-known magneto-oscillations in transport measurements. They are caused by Landau quantization of two-dimensional (2D) electron systems in the presence of a magnetic field. Here we demonstrate that a scanning tunneling microscope (STM) can locally measure similar magneto-oscillations in 2D systems. In Landau level spectroscopy measurements with fine magnetic-field increments, we observed fixed-energy magnetic-field-dependent oscillations of the local density of states. From the measured tunneling magneto-conductance oscillations acquired by STM, energy-momentum dispersions and Berry phases of a monolayer, Bernal-stacked bilayer, and ABC-stacked trilayer graphene were obtained. The reported method is applicable to a wide range of materials because it can obtain the magneto-oscillations of 2D systems larger than the magnetic length; importantly, it also requires no gate electrode.

The isostructural and isoelectronic transition-metal-dichalcogenides 1T-TaS2 and 1T-TaSe2 are layered materials with intricate electronic structures. Combining the molecular beam epitaxy growth, scanning tunneling microscopy measurements and first-principles calculations, we prepare monolayer 1T-TaS2 and TaSe2 and explore their electronic structures at the atomic scale. Both two-dimensional (2D) compounds exhibit commensurate charge density wave phase at low temperature. The conductance mapping identifies the contributions from different Ta atoms to the local density of states with spatial and energy resolution. Both 1T-TaS2 and 1T-TaSe2 monolayer are shown to be insulators, while the former has a Mott gap and the latter is a regular band insulator.

Fluorescent molecules are highly susceptible to their local environment. Thus, a fluorescent molecule near a plasmonic nanoparticle can experience changes in local electric field and local density of states that reshape its intrinsic emission spectrum. By avoiding ensemble averaging while simultaneously measuring the super-resolved position of the fluorophore and its emission spectrum, single-molecule hyperspectral imaging is uniquely suited to differentiate changes in the spectrum from heterogeneous ensemble effects. Thus, we uncover for the first time single-molecule fluorescence emission spectrum reshaping upon near-field coupling to individual gold nanoparticles using hyperspectral super-resolution fluorescence imaging, and we resolve this spectral reshaping as a function of the nanoparticle/dye spectral overlap and separation distance. We find that dyes bluer than the plasmon resonance maximum are red-shifted and redder dyes are blue-shifted. The primary vibronic peak transition probabilities shift to favor secondary vibronic peaks, leading to effective emission maxima shifts in excess of 50 nm, and we understand these light-matter interactions by combining super-resolution hyperspectral imaging and full-field electromagnetic simulations.

We studied surface corrosion effects on Zr and UN using first-principles density functional theory-based calculations. We focused on the energetics of Zr (1000), UN (100) and UN (110) surfaces, exposed to water and oxygen. Average distance between the terminating UN (100) surface and bulk increases due to the presence of additional oxygen content, as well as for the (110) surface. The average distance between the surface layer and bulk is greater in the (110) surface than the (100) surface after water adsorption. Oxygen concentration determines whether H2 or oxynitrde is formed on the (110) surface. Local density of states and partial charge density show the bonding between the UN surfaces and adsorbates. From an electronic energy of −2 eV to the Fermi level, the majority of electrons are found to be localized around U atoms. Electron localization function calculations further reveal the corrosion mechanism details.

Interface engineering of CdS/CZTS(Se) is an important aspect of improving the performance of buffer/absorber heterojunction combination. It has been demonstrated that the crossover phenomenon due to the interface recombination can be drastically eliminated by interface modification. Therefore, in-depth studies across the CdS/CZTS(Se) junction properties, as well as effective optimization processes, are very crucial for achieving high-efficiency CZTSSe solar cells. Here, we present a comprehensive study on the effects of soft-baking (SB) temperature on the junction properties and the corresponding optoelectronic and interface-structural properties. Based on in-depth photoemission studies corroborated with structural and composition analysis, we concluded that interdiffusion and intermixing of CZTSSe and CdS phases occurred on the Cu-poor surface of CZTSSe at elevated SB temperatures, and the interface dipole moments induced by electrostatic potential fluctuation were thus significantly eliminated. In contrast, with low SB temperature, the CdS/CZTSSe heterojunction revealed very sharp interface with very short interdiffusion, forming interface dipole moments and drastically deteriorating device performance. These post thermal treatments also significantly suppress defect energy level of interface measured by admittance spectroscopy from 294 to 109 meV due to CdS/CZTSSe interdiffusion. Meanwhile, the interdiffusion effects on the shift of valence band maximum, conduction band minimum and band offset across the heterojunction of thermally treated CdS/CZTSSe interface are spatially resolved at the atomic scale by measuring the local density of states with cross-sectional scanning tunneling microscopy and spectroscopy. A significant enhancement in the power conversion efficiency from 4.88% to 8.48% is achieved by a facile interface engineering process allowing a sufficient intermixing of CdS/Cd and CZTSSe/Se phases without detrimental recombination centers.

The photoluminescence quantum yield characterizes the performance of emitters for applications in optical devices, as reporters or probes in material and analytical sciences, and for sensing applications. Quantum yield measurements are challenging for luminescent molecules and nanocrystals immobilized in thin films for many sensor applications, particularly if spatially resolved quantitative luminescence information is desired. We show here that a Drexhage-type experiment, where a silver-coated millimeter-sized sphere is used to modify the local density of states, can provide an elegant approach to counter this challenge. As a representative example of the potential of this method, we measure the pH-dependent photoluminescence quantum yield of fluorescein isothiocyanate bound to a thin mesoporous silica film. The results were compared with those of the studies on the pH dependence of the same dye in solution. We found that our approach can link single fluorophore studies to ensemble measurements and pave ...

Nanoscale heterostructure engineering is the main target for the development of optoelectronic devices. In this sense, a precise knowledge of local electronic response after materials processing is...

Flower defect in graphene is observed in the experiment and can be generated by electron beam exposure. In this work, we investigate the spin-polarized transport through zigzag graphene nanoribbons containing a flower defect by using nonequilibrium Green’s functions in combination with the density functional theory. We found high spin polarization in Zigzag Graphene Nanoribbon (ZGNR) with a flower defect. The dependence of spin polarization on the width of ZGNR is also studied. The underlying mechanism is analyzed through the flower defect–induced different distributions of spin up and spin down local density of states.

In this paper, we study electrical properties of AB-stacked bilayer graphene-DNA hybrid nanostructure connected to two semi-infinite monolayer graphene nanoribbon leads. We investigated two types of devices with both zigzag and armchair edges and the results are evaluated by replacing the junction position. Our calculations are based on the tight-binding approximation and the Green's function method in which the electrical transmission, the density of states (DOS) and the local density of states (LDOS) are calculated numerically. In the metallic bilayer graphene device via creating a nanopore and translocating the DNA molecule, the electron transmission reduces and an energy gap opens, so that, the metal-semiconductor phase transition occurs. Also, our results indicate that the model AC leads to a more considerable energy gap than model AB. Our results have important applications in DNA sensing.

We studied the valley dependent transport in a T junction consisting of an armchair lead and two zigzag leads. Electrons transmitted from the armchair lead to the two outgoing zigzag leads can be valley polarized. When the two outgoing leads have different widths, electrons are pushed into the wider lead and as a result, the valley polarization of the current in the narrow lead is enhanced with an oscillatory dependence on energy. The oscillation pattern is determined by the widths of the two zigzag leads. We analyzed the total local density of states of the device region of the junction and cannot find features that attribute this enhancement to quasi-bound state formation.

By applying scanning tunneling microscope (STM), we directly observed the coexistence of superconductivity and Moire pattern on Se terminated surface of PbTaSe2. Two different Moire periodicities with 9.7 and 24 times of the crystal lattice were observed and the Moire patterns showed distinct characters at different sample biases. Scanning tunneling spectroscopy (STS) studies revealed that the electronic structures were greatly modified by the Moire patterns, and Moire patterns with different manifestations had distinct electronic structures outside the superconducting (SC) gap. The main difference of the electronic structures of the bright and dark area of the Moire pattern is a 1 meV energy shift of the peak positions on the local density of states (LDOS). We argued that the interlayer chemical bond and the multiple rotation conditions at the surface were responsible for the various manifestations of Moire patterns and the great modifications of electronic structures. On surfaces with different Moire patterns, the SC gaps are only slightly changed and remains homogeneous across the surfaces, which indicates that the proximity effect is the origin of superconductivity on Se surfaces.

Structural and electronic properties of bilayer graphene films and nanostructures obtained through the graphitization of SiC(0001) were investigated in this work using scanning tunneling microscopy and spectroscopy. We report on the observation of triangular nanostructures which result from extended stacking faults in the SiC substrate and their effects on graphene layers that are formed on top of them. Spectroscopic measurements revealed distinct electronic responses as a function of the local hydrogen intercalation. Spectroscopic signatures ranging from single- to double-layer graphene, as well as intermediate states were observed as a consequence of the (in)complete hydrogen intercalation process. High resolution topographic scanning tunneling microscopy images at resonant bias voltages inside triangular nanostructures reveal that the bottom layer of the bilayer graphene film is still bonded to the substrate. Therefore, the triangular nanostructures present edges and facets with the coexistence of carbon atoms in sp3 and sp2 hybridizations. Using atomistic calculations we have modeled the local density of states of these objects reproducing their electronic response. The generation of regions with distinct electronic responses is potentially interesting for high-density data storage with hidden bit capabilities., The authors acknowledge experimental support by the Brazilian Synchrotron Light Laboratory (LNLS). Financial support was provided by CNPq, CAPES, FAPEMIG and INCT-Nano-Carbono. This work was partially financed by the Project FIS2016-76617-P of the Spanish Ministry of Economy and Competitiveness MINECO, the Basque Government under the ELKARTEK project (SUPER), and the University of the Basque Country (Grant No. IT-756-13).