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We investigate the behavior of vortex bound states in the quantum limit by self-consistently solving the Bogoliubov-de Gennes equation. We find that the energies of the vortex bound states deviates from the analytical result $E_\mu=\mu\Delta^2/E_F$ with the half-integer angular momentum $\mu$ in the extreme quantum limit. Specifically, the energy ratio for the first three orders is more close to $1:2:3$ instead of $1:3:5$ at extremely low temperature. The local density of states reveals an Friedel-like behavior associated with that of the pair potential in the extreme quantum limit, which will be smoothed out by thermal effect above a certain temperature even the quantum limit condition, namely $T/T_c, Comment: 4 pages, 5 figures

Color centers in hexagonal boron nitride (hBN) have emerged as promising candidates for single-photon emitters (SPEs) due to their bright emission characteristics at room temperature. In contrast to mono- and few-layered hBN, color centers in multi-layered flakes show superior emission characteristics such as higher saturation counts and spectral stability. Here, we report a method for determining both the axial position and three-dimensional dipole orientation of SPEs in thick hBN flakes by tuning the photonic local density of states using vanadium dioxide (VO2), a phase change material. Emitters under study exhibit a strong surface-normal dipole orientation, providing some insight on the atomic structure of hBN SPEs, deeply embedded in thick crystals. We have optimized a hot pickup technique to reproducibly transfer flakes of hBN from VO2 onto SiO2/Si substrate and relocated the same emitters. Our approach serves as a practical method to systematically characterize SPEs in hBN prior to integration in quantum photonics systems., 33 pages, 5 figures, 1 Table, and 13 supplementary figures

Weyl semimetals are prominent examples of topologically protected quantum matter. These materials are the three-dimensional counterparts of graphene and great efforts are being devoted to achieve a thorough understanding of their fundamental physics. In this work, we aim at contributing to this end by discussing the effect of a single magnetic impurity in Weyl semimetals as a first step towards considering a larger number of point-like impurities. We find that resonances appear in the local density of states (LDOS) with a Friedel-like behaviour, oscillating as a function of distance. By studying the spin-resolved LDOS, we can observe non-trivial and anisotropic spin textures where the spin components perpendicular to the spin of the impurity wind around the latter, until the spin becomes completely parallel to the impurity right at the impurity’s location. Friedel oscillations also play a relevant role in the form of the spin textures, forming an oscillatory pattern. We believe our results can pave the way to further studies which consider the presence of a large number of random magnetic impurities.

Graphene-based moir\'{e} systems have attracted considerable interest in recent years as they display a remarkable variety of correlated phenomena. Besides insulating and superconducting phases in the vicinity of integer fillings of the moir\'{e} unit cell, there is growing evidence for electronic nematic order both in twisted bilayer graphene and twisted double-bilayer graphene (tDBG), as signaled by the spontaneous breaking of the threefold rotational symmetry of the moir\'{e} superlattices. Here, we combine symmetry-based analysis with a microscopic continuum model to investigate the structure of the nematic phase of tDBG and its experimental manifestations. First, we perform a detailed comparison between the theoretically calculated local density of states and recent scanning tunneling microscopy data [arXiv:2009.11645] to resolve the internal structure of the nematic order parameter in terms of the layer, sublattice, spin, and valley degrees of freedom. We find strong evidence that the dominant contribution to the nematic order parameter comes from states at the moir\'{e} scale rather than at the microscopic scale of the individual graphene layers, which demonstrates the key role played by the moir\'e degrees of freedom and confirms the correlated nature of the nematic phase in tDBG. Secondly, our analysis reveals an unprecedented tunability of the orientation of the nematic director in tDBG by an externally applied electric field, allowing the director to rotate away from high-symmetry crystalline directions. We compute the expected fingerprints of this rotation in both STM and transport experiments, providing feasible ways to probe it. Rooted in the strong sensitivity of the flat bands of tDBG to the displacement field, this effect opens an interesting route to the electrostatic control of electronic nematicity in moir\'{e} systems., Comment: 21 pages, 10 figures

In this study, the density functional theory (DFT) is used to investigate the effects of passivating line sulfur vacancies by non-metal species (C, N, O, F, OH and NH2) in armchair MoS2 nanoribbon (AMoS2NR) on its structural, electrical and optical properties. Calculated binding energies show that passivation of line vacancies by oxygen atoms leads to the most stable structures. Electronic calculations show that presence of single line vacancies decreases the bandgap of 0.68 eV in perfect AMoS2NR to 0.62 eV in single line vacant AMoS2NR (SV) and substituting the vacancies with carbon and oxygen (C-SV and O-SV) returns the bandgap to its initial value. It is also shown that passivation of SV with NH2 leads to a semiconductor with a small bandgap of 0.08 eV. However, substituting the vacancies of SV with N, F and OH results in metallic structures. In the case of double line vacant AMoS2NR (DV), the bandgap reduces significantly (0.38 eV) with respect to its perfect counterpart. Similar to what happened in SV, passivating DV with C and O again increases the bandgap to the bandgap of the perfect structure. Furthermore, N-, F-, OH- and NH2-DV show metallic behavior. In addition, we use total, projected and local density of states (TDOS, PDOS and LDOS) analysis to reveal the role of different atoms in different positions on the electronic properties of defective AMoS2NRs. In order to investigate the effect of passivation on the optical properties of defective AMoS2NRs we present the real and imaginary parts of dielectric function spectra. Our results suggest that passivation of line vacancies by different atoms can efficiently tune the absorption of AMoS2NR and open a new path to obtain MoS2-based optoelectronic devices.

The adsorption and gas sensing properties of black arsenene (B-As) regarding sulfur hexafluoride (SF6) and its six decompositions (SOF2, SO2F2, SO2, H2S, HF, and CF4) are investigated using density functional theory combined with the nonequilibrium Green’s function. The sensitivity of B-As is evaluated by considering the most stable adsorption configuration, adsorption energy, work function, recovery time, local density of states, and charge transfer between the gas molecules and B-As. It is demonstrated that B-As is more sensitive to the SO2 molecule than to the other decompositions. Additionally, the adsorption strength can be manipulated by controlling the external electric field (E-field). The application of tensile biaxial strain results in more isotropic electrical conductance of B-As, and it can also effectively enhance the response toward SO2. For example, under a 1% equibiaxial tensile strain, a 132% response can be obtained along the zigzag direction. This work suggests the promising prospects of B-As-based gas sensors for detecting SO2 among SF6 decompositions.

By analytically solving the Bogoliubov–de Gennes equations we study the fermion bound states at the center of the core of a vortex in a two-dimensional superconductor. The superconducting states are induced via proximity effect between an s-wave superconductor and the surface states of a strong topological insulator. The strong spin–orbit coupling locks the spin perpendicular to the momentum (Rashba interaction). A zero-energy Majorana state arises together with an equally spaced ( Δ ∞ 2 / E F ) sequence of fermion excitations. The spin–momentum locking is key to the formation of the Majorana state. We present analytical expressions for the energy spectrum and the wave functions of the bound states. The wave functions fall off exponentially with the distance ρ from the core of the vortex as exp [ − ∫ 0 ρ d ρ ′ Δ ( ρ ′ ) / v F ] . An analytic expression for the local density of states (LDOS) for the bound states is obtained. The particle–hole symmetry is broken in the LDOS as a consequence of the spin–orbit coupling. The spin-polarization of the bound states is discussed. We also obtain the energy shifts of the bound states in a small magnetic field. A unitary transformation relating the model with Rashba interaction to the Dirac Hamiltonian is presented.

The complete set of Eigenstates and Eigenvalues of the nearest neighbour tight binding model on a Cayley tree with branching number $b=2$ and $M$ branching generations with open boundary conditions is derived. We find that of the $N= 1 +3 (2^M-1)$ total states only $3 M +1$ states are extended throughout the Cayley tree. The remaining $N-(3 M+1)$ states are found to be strongly localised states with finite amplitudes on only a subset of sites. In particular, there are, for $M>1$, $3 \times 2^{M-2}$ surface states which are each antisymmetric combinations of only two sites on the surface of the Cayley tree and have energy eactly at $E=0$, the middle of the band. The ground state and the first two excited states of the Cayley tree are found to be extended states with amplitudes on all sites of the Cayley tree, for all $M$. We use the results on the complete set of Eigenstates and Eigenvalues to derive the total density of states and a local density of states., 8 pages, 7 figures

Chern insulators (CIs) or quantum anomalous Hall (QAH) states have drawn more attention, with emergence of quantized Hall conductance but in absence of Landau levels. Here, we study the Haldane-type CI/QAH states on Möbius strips and focus on the quantum transport properties. The Möbius strips can be constructed from the twisted honeycomb-lattice strips with domain walls. Topological properties of the Möbius CI/QAH states can be identified by the local density of states, the real-space Chern numbers and the transport properties. Nearly perfect quantized conductance plateaus are observed in the numerical quantum-transport simulations. In addition, we found that adding magnetic flux in domain walls can induce alternating edge states. At last, we discussed in details the different lead connection schemes, and found that we can use multiple domain walls to obtain various higher quantized conductance plateaus.

A detailed understanding of interacting electrons in twisted bilayer graphene (tBLG) near the magic angle is required to gain insights into the physical origin of the observed broken symmetry phases including correlated insulator states and superconductivity. Here, we present extensive atomistic Hartree theory calculations of the electronic properties of tBLG in the (semi-)metallic phase as function of doping and twist angle. Specifically, we calculate quasiparticle properties, such as the band structure, density of states (DOS) and local density of states (LDOS), which are directly accessible in photoemission and tunnelling spectroscopy experiments. We find that quasiparticle properties change significantly upon doping - an effect which is not captured by tight-binding theory. In particular, we observe that the partially occupied bands flatten significantly which enhances the density of states at the Fermi level and explains the experimentally observed Fermi level pinning. We predict a clear signature of this band flattening in the LDOS in the AB/BA regions of tBLG which can be tested in scanning tunneling experiments. We also study the dependence of quasiparticle properties on the dielectric environment of tBLG and discover that these properties are surprisingly robust as a consequence of the strong internal screening. Finally, we present a simple analytical expression for the Hartree potential which enables the determination of quasiparticle properties without the need for self-consistent calculations.

We have solved the Bogoliubov-de Gennes equation with a random impurity potential Vimp(r) under an external magnetic field with the finite element method and obtained the local density of states and the order parameter around a vortex. From these results, we find two properties of a vortex structure in a dirty superconductor. First, the order parameter structure around the vortex is deformed by the impurity potential. Second, distributions of bound states is also deformed, but these deformations of the order parameter and bound states do not correspond with each other.

In nano-structured superconductors, it is important to consider a discreteness of energy levels instead of continuous energy levels due to the quantum confinement effect. This discreteness causes an appearance of many peaks in a density of state (DOS). In this paper, the effect of the discreetness of energy level or the effect of the quantum confinement on the DOS in superconducting systems with superconductor / normal metal (S/N) interfaces are focused. In particular, in nano-sized finite systems, a local density of state (LDOS) becomes strongly spatial dependent because of non-uniform spatial distributions of a gap energy and a pair amplitude. We investigate the pair amplitude and the LDOS by solving the Bogoliubov-de Gennes equations self-consistently. The proximity effect leads to a penetration of the pair amplitude into the normal metal region. Then, the pair amplitude in the normal metal decays non-monotonously because of the effect of the nano-sized finite system. On the other hand, the spatial-averaged LDOS plots as a function of the energy have many peaks in both superconductor and normal metal regions. Also, a contribution of the normal metal to the superconductor causes an appearance of peaks of the LDOS at the energy below the gap energy. In the SNS junction, when width of the normal metal increases, these peaks at the energy below the gap energy appear clearly.

Using the first-principles calculations, we study the structural, electronic, and magnetic properties along with exchange interactions and Curie temperatures for CrZrCoZ (Z = Al, Ga, In, Tl, Si, Pb) quaternary Heusler alloys. The results show that the CrZrCoZ alloys are half-metallic ferrimagnets, and their total spin magnetic moments, which are mainly carried by the Cr atom, obey the Slater–Pauling rule. Analysis of local density of states confirms that the exchange splitting between eg and t2g states leads to the formation of half-metallic gap. According to the calculated Heisenberg exchange coupling parameters, it is found that the Cr(A)–Cr(A) and Cr(A)–Zr(B) exchanges dominate the appearance of ferrimagnetic states in CrZrCoZ (Z = Al, Ga, In, Tl, Pb) alloys, and it is the Cr(A)–Zr(B) and Zr(B)–Zr(B) exchanges for CrZrCoSi alloy. Finally, we estimate the Curie temperatures of CrZrCoZ by using mean-field approximation, it is found that the CrZrCoZ (Z = Al, Ga, In, Tl, Pb) alloys have noticeably higher Curie temperatures than room temperature. So, we expect that the CrZrCoZ alloys are promising candidates in spintronic applications in future.

In the search of high-temperature superconductivity one option is to focus on increasing the density of electronic states. Here we study both the normal and $s$-wave superconducting state properties of periodically strained graphene, which exhibits approximate flat bands with a high density of states, with the flatness tunable by the strain profile. We generalize earlier results regarding a one-dimensional harmonic strain to arbitrary periodic strain fields, and further extend the results by calculating the superfluid weight and the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_\text{BKT}$ to determine the true transition point. By numerically solving the self-consistency equation, we find a strongly inhomogeneous superconducting order parameter, similarly to twisted bilayer graphene. In the flat band regime the order parameter magnitude, critical chemical potential, critical temperature, superfluid weight, and BKT transition temperature are all approximately linear in the interaction strength, which suggests that high-temperature superconductivity might be feasible in this system. We especially show that by using realistic strain strengths $T_\text{BKT}$ can be made much larger than in twisted bilayer graphene, if using similar interaction strengths. We also calculate properties such as the local density of states that could serve as experimental fingerprints for the presented model., Comment: 14+15 pages, 12+2 figures. Corrected the BKT transition temperature estimates in the end

We construct an artificial neural network to study the pairing symmetries in disordered superconductors. For Hamiltonians on square lattice with s-wave, d-wave, and nematic pairing potentials, we use the spin-polarized local density of states near a magnetic impurity in the clean system to train the neural network. We find that, when the depth of the artificial neural network is sufficient large, it will have the power to predict the pairing symmetries in disordered superconductors. In a large parameter regime of the potential disorder, the artificial neural network predicts the correct pairing symmetries with relatively high confidences.

Electronic Whispering Gallery Modes (EWGMs) have been recently observed in several circular graphene junctions, pn and pp0, created in scanning tunnelling microscope experiments. By computing the local density of states within the Dirac-Weyl formalism for massless fermions we demonstrate that the EWGMs may really be emerged in any type of the electrostatic potential induced circular graphene junctions, including uni-junctions (e.g. np- or pp0-junctions) as well as bipolar-junctions (e.g. pnp-heterojunctions). Surprisingly, quantitative analyses show that for all the EWGMs identified (regardless of junction types) the quality (Q) factors seem to be smaller than 100, very small compared to those in ordinary optical whispering gallery modes microresonators, while the corresponding mode radii may tunably be in nanometer-scale. Our theoretical results are in good agreement with existent experimental data, putting a question to the application potential of the EWGMs identified., Comment: It is 9 pages long, 6 figures

We present a simple view on band unfolding of the energy bands obtained from supercell calculations. It relies on the relationship between the local density of states in reciprocal space (qLDOS) and the fully unfolded band structure. This provides an intuitive and valid approach not only for periodic, but also for systems with no translational symmetry. By refolding into the primitive Brillouin zone of the pristine crystal we recover the conventional unfolded bands. We implement our algorithm in the SIESTA package and apply it to defects on Si and graphene., Comment: 8 pages, 10 figures

Electronic structure calculations for a homo-material semimetal (thick Sn)/semiconductor (thin Sn) heterodimensional junction and two conventional metal (Ag or Pt)/silicon hetero-material junctions are performed. Charge distributions and local density of states are examined to compare the physics of junctions formed by quantum confinement in a homo-material, heterodimensional semimetal junction with that of conventional Schottky hetero-material junctions. Relative contributions to the Schottky barrier heights are described in terms of the interface dipoles arising due to charge transfer at the interface and the effects of metal induced gap states extending into the semiconducting regions. Although the importance of these physical mechanisms vary for the three junctions, a single framework describing the junction energetics captures the behaviors of both the heterodimensional semimetal junction and the more conventional metal/semiconductor junctions.

As the devices approach their scaling limit, finding new material or technology for next generation nano-devices becomes one of the most important tasks in the modern electronics industry. Here, based on the first principles calculations, we have systematically studied the effects of gate voltages on black phosphorus/blue phosphorus (black-P/blue-P) van der Waals heterojunction (vdWh). Our results show that the black-P/blue-P vdWh can transform from a semiconductor to a metal when the gate voltage is strong enough. In addition, the local density of states at the Fermi level are mainly localized either in the topmost or bottom layer depending on the gate voltage. Based on these properties, a two-gated device is proposed. By changing the directions of the applied gate voltages on electrodes, the device can realize 'ON' or 'OFF' states. The calculated transmission coefficient of black-P/blue-P vdWh is sensitive to the direction of the two gate voltages, which can be understood based on the distribution of electrons on different atomic layers and asymmetric structure in the heterojunction. These findings may serve as guidance for designing novel devices with improved performance based on 2D materials.

Symmetry breaking in graphene has profound impacts on its physical properties. Here we emulate symmetry breaking in artificial graphene systems by assembling coronene molecules on a Cu(111) surface. We apply two strategies: (1) differentiating the on-site energy of two sublattices of a honeycomb lattice and (2) uniaxially compressing a honeycomb lattice. The first one breaks the inversion symmetry while the second one merges the Dirac cones. The scanning tunneling spectroscopy shows that in both cases the local density of states undergo characteristic changes. Muffin-tin simulations reveal that the observed changes are associated with a band gap opened at the Dirac point. Furthermore, we propose that using larger molecules or molecules strongly scattering the surface state electrons can induce an indirect gap.

The electrostatic gating defined channel in graphene forms a charge carrier guider. We theoretically investigated electronic transport properties of a single channel and an Aharanov-Bohm (AB) interferometer, based on a charge carrier guider in a graphene nanoribbon. Quantized conductance is found in a single channel, and the guider shows high efficiency in the optical fiber regime, in good agreement with the experiment results. For an AB interferometer without a magnetic field, quantized conductance occurs when there are a few modes inside the channel. The local density of states (LDOS) inside the AB interferometer shows quantum scars when the scattering is strong. At low magnetic field, a periodical conductance oscillation appears. The conductance has a maximum value at zero magnetic field in the absence of intravalley scattering. The mechanism was investigated by LDOS calculations and a toy model.

Kondo transport properties through a Kondo-type quantum dot (QD) with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green's function method. We firstly derive the formulae of the current, the linear conductance, the transmission coefficient, and the local density of states. Then we carry out the analytical and numerical studies and some universal conductance properties are obtained. It is shown that the number of the conductance valleys is intrinsically determined by the side-coupled QDs and at most equal to the number of the QDs included in the side-coupled structure in the asymmetric limit. In the process of forming the conductance valleys, the side-coupled QD system plays the dominant role while the couplings between the Kondo-type QD and the side-coupled structure play the subsidiary and indispensable roles. To testify the validity of the universal conductance properties, another different kinds of side-coupled triple-QD structures are considered. It should be emphasized that these universal properties are applicable in understanding this kind of systems with arbitrary many-QD side structures.

International audience; We present an inhomogeneous dynamical mean field theory (I-DMFT) that is suitable to investigate electron-lattice interactions in non-translationally invariant and/or inhomogeneous systems. The presented approach, whose only assumption is that of a local, site-dependent self-energy, recovers both the exact solution of an electron for a generic random tight-binding Hamiltonian in the non-interacting limit and the DMFT solution for the small polaron problem in translationally invariant systems. To illustrate its full capabilities, we use I-DMFT to study the effects of defects embedded on a two-dimensional surface. The computed maps of the local density of states reveal Friedel oscillations, whose periodicity is determined by the polaron mass. This can be of direct relevance for the interpretation of scanning-tunneling microscopy (STM) experiments on systems with sizable electron-lattice interactions. Overall, the easy numerical implementation of the method, yet full self-consistency, allows one to study problems in real-space that were previously difficult to access.

We demonstrate strongly polarized photoluminescence (PL) from Er3+ ions embedded in plasmonic nanocavity arrays, which was reported in our recent paper [Choi et al., Nano Lett. 16, 5191 (2016)]. The precise positioning of the Er3+ layer within the nanocavities with respect to the node and antinode of the electromagnetic field modifies the PL spectral shape and allows linearly polarized emission with a 98% degree of polarization. The observed PL is caused by a single component of the dipole moments in Er3+ emitters and by anisotropically controlled local density of states.

We report results for the electronic structure of irradiated and irradiation-induced amorphized graphene based on first-principles density functional theory calculations, using models of irradiated graphene sheets that were initially relaxed structurally according to molecular-dynamics simulations. We find that localized states appear at the Fermi level upon irradiation damage and the corresponding local density of states increases with increasing defect density. Electronic structure calculations show that band flattening occurs due to electron localization in the vicinity of irradiation-induced defects and reduces the charge carrier mobility. This band flattening effect becomes stronger with increasing defect density due to a greater degree of carrier localization at irradiation-induced carbon dangling bonds. Passivating these dangling bonds with hydrogen atoms delocalizes the charge density, reduces the density of states at the Fermi level, and increases the band dispersion. Hydrogen passivation also has the additional effect of quenching any localized magnetic moments at dangling bonds. Our studies show that defect engineering of graphene—even at a gross level without atomic-scale precision—can be employed to tune its properties for additional electronic functionality.

The local electronic states around a single As (Te, Se) vacancy are investigated in order to shed light on the role of ligands in a series of iron-based superconductors. Such a vacancy can produce a local hopping correction ranging from $-0.22$ eV to 0.12 eV and always induce two in-gap resonance peaks in the local density of states (LDOS) at the fixed symmetrical bias voltages, which are rather robust and irrelevant to the phase of superconducting order parameter. The LDOS images near the defect predominantly possess $0^o$ and $45^o$ stripes. These energy-dependent charge modulations created by quasiparticle interference are originated in the nesting effect between the inner (outer) hole Fermi surface around $\Gamma$ point and the inner (outer) electron Fermi surface around $M$ point., Comment: 4 pages, 5 figures

Nonuniform strain in graphene induces a position dependence of the Fermi velocity, as recently demonstrated by scanning tunnelling spectroscopy experiments. In this work, we study the effects of a position-dependent Fermi velocity on the local density of states (LDOS) of strained graphene, without and with the presence of a uniform magnetic field. The variation of LDOS obtained from tight-binding calculations is successfully explained by analytical expressions derived within the Dirac approach. These expressions also rectify a rough Fermi velocity substitution used in the literature that neglects the strain-induced anisotropy. The reported analytical results could be useful for understanding the nonuniform strain effects on scanning tunnelling spectra of graphene, as well as when it is exposed to an external magnetic field., Revised version as published in JPCM

The quantum electronic transport through a precessing magnetic spin coupled to noncollinearly polarized ferromagnetic leads (F-MS-F) has been studied in this paper. The nonequilibrium Green function approach is used to calculate local density of states (LDOS) and current in the presence of external bias. The characters of LDOS and the electronic current are obtained. The tunneling current is investigated for different precessing angle and different configurations of the magnetization of the leads. The investigation reveals that when the precessing angle takes θ < π/2 and negative bias is applied, the resonant tunneling current appears, otherwise, it appears when positive bias is applied. When the leads are totally polarized and the precessing angel takes 0, the tunneling current changes with the configuration of two leads; and it becomes zero when the two leads are antiparallel.

Using the nonequilibrium Green's function technique, we investigate the Kondo effect in the quantum dot with perpendicular magnetic fields, in which one is the Zeeman splitting lies in the z-direction and the other is the spin flip points at the x-direction. It is found whatever one or two magnetic fields are applied, the local density of states (LDOS) will split into two peaks. The positions of two Kondo resonance peaks are determined by Zeeman energy Δ when J = 0, and by when J ≠ 0.

Ag adsorptions at 0.25-3 monolayer (ML) coverage on a perfect TiC(001) surface and at 0.25ML coverage on C vacancy are separately investigated by using the pseudopotential-based density functional theory. The preferential adsorption sites and the adsorption-induced modifications of electronic structures of both the substrate and adsorbate are analysed. Through the analyses of adsorption energy, ideal work of separation, interface distance, projected local density of states, and the difference electron density, the characteristic evolution of the adatom-surface bonding as a function of the amount of deposited silver is studied. The nature of the Ag/TiC bonding changes as the coverage increases from 0.25 to 3 MLs. Unlike physisorption in an Ag/MgO system, polar covalent component contributes to the Ag/TiC interfacial adhesion in most cases, however, for the case of 1-3 ML coverage, an additional electrostatic interaction between the absorption layer and the substrate should be taken into account. The value of ideal work of separation, 1.55 J/m(2), for a 3-ML-thick adlayer accords well with other calculations. The calculations predict that Ag does not wet TiC(001) surface and prefers a three-dimensional growth mode in the absence of kinetic factor. This work reports on a clear site and coverage dependence of the measurable physical parameters, which would benefit the understanding of Ag/TiC(001) interface and the analysis of experimental data.

In the present paper, by applying the Lang–Firsov canonical transformation and the so-called non-crossing approximation technique, we investigate the joint effects of the electron-phonon interaction and an external alternating gate voltage on the transport of a quantum dot system in the Kondo regime. We find that, while the satellite Kondo resonant peaks appear in both the averaged local density of states and the differential conductance, the main Kondo peak at the Fermi energy is greatly suppressed. These results confirm the previous ones derived by other methods, such as the equation of motion solution. Furthermore, based on the picture of virtual transition between quasi-eigenstates in the system, we also give a slightly different explanation on these phenomena.

We study electronic transport through a quantum dot (QD) with a precessing magnetic field. By using the Keldysh nonequilibrium Green function method, formulas of local density of states (LDOS) and conductance of QD are derived self-consistently. It shows that the LDOS and conductance have obvious changes with the Coulomb blockade interaction. The intensity and angle of the magnetic field or temperatures, which reflect the mesoscopic structure of the QD are derived. The superiority of this device is that the QD can be controlled easily by the magnetic field, so it is valuable to apply in generating, manipulating and probing spin state.

Si nanocrystals (NCs) were embedded in synthetic silica opals by means of Si-ion implantation or opal impregnation with porous-Si suspensions. In both types of sample photoluminescence (PL) is strongly Bragg-reflection attenuated (up to 75%) at the frequency of the opal stop-band in a direction perpendicular to the (1 1 1) face of the perfect hcp opal structure. Time-resolved PL shows a rich distribution of decay rates, which contains both shorter and longer decay components compared with the ordinary stretched exponential decay of Si NCs. This effect reflects changes in the spontaneous emission rate of Si NCs due to variations in the local density of states of real opal containing defects.

We measure the spatial variation of the local density of states normal to an InAs/GaSb heterointerface on a cleaved cross-sectional surface by low-temperature scanning tunneling spectroscopy. Clear standing waves originating from the interference between the incident and reflected electron waves at the interface are observed.

We performed ab-initio density functional calculations to study the structural and growth properties of short carbon nanobells. We used a real space approach and the linear combination of atomic orbitals (LCAO) formalism. In the nitrogen-doped carbon nanobells, the nitrogen atoms that are attracted to the open-edge sites of the carbon nanobells play an important role in the growth of the short carbon nanostructures. We present the calculated electronic structure of the short nanobells. The calculated local density of states of the nanobells revealed field emission characteristics that agree with experimental observations.

Low-temperature scanning tunneling spectroscopy under ultra-high vacuum was employed to investigate the two-dimensional electron system at the epitaxial surface of Sidoped In0.53Ga0.47As/In0.52Al0.48As(111)A quantum-well structures. The electron density in the near-surface region of the quantum well could be controlled through modulation doping. Spectra of the electronic local density of states in the conduction band showed a clear step-like energy dependence that reveals the subband states. In spectra acquired at some areas of nanometer size, peaks were observed near subband minima, indicating the existence of bound states.

The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs substrate was studied at very low temperatures in magnetic fields up to 6 T by scanning tunneling microscopy and spectroscopy. We observed a series of peaks, associated with Landau quantization of the two-dimensional electron system (2DES), in the tunnel spectra just above the subband energy (-80 meV) of the 2DES. The intervals between the peaks are consistent with the estimation from the effective mass of the 2DES at the InAs surface. In a wider energy range, another type of oscillation which was independent of magnetic field was also observed. This oscillation can be explained by the energy dependence of the transmission probability of the tunneling current through the Schottky barrier formed at the interface between the InAs film and GaAs substrate.

We report the observation on the charge ordering of Fe ions in a magnetite(Fe3O4)(001) film surface by scanning tunneling microscopy and spectroscopy (STM/STS) with a nonmagnetic W tip. The Fe3O4(001) film surface exhibits a B-plane termination with a (√2 × √2)R45° reconstruction. Fe cation rows running along the [110] direction show a wavelike structure. The (√2 × √2)R45° surface reconstruction is originated from the wavelike Fe rows. The current imaging tunneling spectroscopy image shows alternation of two different kinds of current peak with a separation of about 0.6 nm. Each current peak arises from the same local density of states (LDOS) of two Fe ions. The presence of Fe dimers with two different kinds of LDOS provides evidence for the charge ordering of Fe ions with different charge states. STM and STS using a nonmagnetic W tip allow us to correlate the charge ordering pattern with the surface structure.

We report on a technique able to create low-energy hydrogen ions induced defects on single walled carbon nanotubes (SWCNT) using a hydrogen electron cyclotron resonance (ECR) plasma source. Low temperature scanning tunneling microscopy (LT-STM) investigations revealed defect sites with hillocks-like features between 1 A and 3 A in height and lateral spreading between 0.5 nm and 2 nm. Scanning tunneling spectroscopy (STS) measurements on a metallic SWCNT revealed a strong modification of the electronic structure on a specific defect zone characterized by a pronounced peak in the local density of states (LDOS) close to the Fermi energy.

A massive Ni tip is used in spin polarized scanning tunnelling microscopy (SP STM) to explore the magnetization state of nanometre Co clusters, self-organized on the Au(111) surface. Constant current STM images taken at 4.6 K show a bimodal distribution of the cluster heights, accounting for the spin polarization of the STM junction. The spin polarization of the tunnel junction as a function of the bias voltage is found to depend on the local density of states of the sample examined. Changing the vacuum barrier parameters by bringing the tip closer to the surface leads to a reduction in the tunnelling magnetoresistance that may be attributed to spin flip effects.

The local density of states (LDOS) and conductance of several (12,0)/(6,6) carbon nanotube junctions (CNTJs) with two substitutional boron atoms have been calculated by the tight-binding model and the Green's function method. It is found that the conductance gap of boron-doped CNTJs changes differently, depending on the different boron positions. For some boron-doped positions, the large conductance gap of undoped CNTJ could disappear completely even if the rotational symmetry is still kept in the doped CNTJs. Our results clearly show that the transport property of a metal–metal CNTJ depends not only on the rotational symmetry of its interface but also on the doped impurity positions on the interface.

This paper introduces a simple model for an atomic nanocontact, where its mechanical properties are analysed by calculating numerically the local spectral properties at the contact atom and the nearby atoms. The standard methodology for calculating phonon spectral densities is extended to enable the calculation of localized contact modes and local density of states (DOS). The model system considered for the nanocontact consists of two sets of triple parallel semi-infinite atomic chains joined by a single atom in between. The matching method is used, in the harmonic approximation, to calculate the local Green's functions for the irreducible set of sites that constitute the inhomogeneous nanocontact domain. The Green's functions yield the vibration spectra and the DOS for the atomic sites. These are numerically calculated for different cases of elastic hardening and softening of the nanocontact domain. The purpose is to investigate how the local dynamics respond to local changes in the elastic environment. The analysis of the spectra and of the DOS identifies characteristic features and demonstrates the central role of a core subset of these sites for the dynamics of the nanocontact. The system models a situation which may be appropriate for contact atomic force microscopy.

We present an implementation of a method to determine different components of the local density of states in the presence of a core hole from inelastic x-ray scattering experiments. The only theoretical input needed beyond experimental data are the embedded atom transition matrix elements. In this work these matrix elements are calculated using a real-space multiple scattering approach. We apply the method to x-ray Raman scattering data for the boron K-edge in MgB2. The capability of the approach is demonstrated by separating the density of π-, σ- and s-type states at the boron site in MgB2.

The tight-binding Hamiltonian and retarded Green function formalism are used to study the local and total density of states of a monatomic quantum wire. An additional atom (adatom) can be coupled with the wire at its side. Also the local and average charges of the perfect and disturbed wire are shown and the analytical formula for the local density of states at each site is obtained. The local density of states at each atom in a wire which consists of an even number of atoms is characterized by minima at the Fermi level, in comparison with a wire disturbed by an adatom, where the density of states is characterized by local peaks. Charge fluctuations (waves) are observed in the wire for the case when the condition for the conductance oscillations is satisfied. For the single electron energies of a wire localized above the Fermi energy the local charge along the wire forms a wave curve which possesses one maximum less than for energies localized below the Fermi level.

The single-particle Green's function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U(t,t') method and Floquet–Green's function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier–Stark states as a result of the intervention of time-dependent impurity potential and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.

The growth and differential conductivity (dI/dV) spectra of ultrathin Fe films on Cr(001) were studied at room temperature (RT) by scanning tunneling microscopy, together with the spin-resolved image of the Cr(001) film. It is found that 2 ML Fe films deposited at RT and postannealed at 300 °C show atomically flat terraces and a distinct peak at +300 mV in the dI/dV spectrum, which corresponds to the spin-polarized surface state of the Fe(001) surface. These features were not observed for submonolayer Fe films on Cr(001) substrates or at postannealing temperatures lower than 200 °C. The spatially resolved dI/dV signal maps of the 2 ML Fe films show a distinct contrast. This contrast may not be of magnetic origin, but a result of the Fe layer dependence of the local density of states.