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

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

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

In this paper, we numerically study the transport properties of a resonant tunneling diode (RTD) based on graphene nanoribbon (GNR) with an H-type antidote between the contacts. The structure may also be thought of as having two parallel (W-shape) parts connecting the contacts, each having a wider channel region sandwiched between two narrower barrier regions. The energy at which quasi-bound states occur in each part depends on the dimensional parameters of the respective portion in the structure. We study how the transmission through quasi-bound states is influenced by the edge states on the contacts and dimensional parameters such as barrier length and also by the ambient temperature. The results are compared with those of an RTD with a single part connecting the contacts. Transmission peaks at different energies are observed for an RTD with asymmetrical lower and upper parts between the contacts. This is then utilized for the creation of two negative differential resistance (NDR) peaks. For numerical computation, the non-equilibrium Green's function formalism (NEGF) based on the nearest neighbor tight-binding model is employed. • Numerical study of RTD based on GNR with an H-type antidote between contacts. • Investigation of transmission through quasi-bound states influenced by edge states, barrier length, and ambient temperature. • Comparison with RTD having a single part connecting contacts. • Observation of two NDR peaks for RTD with asymmetrical lower and upper parts. • Utilization of NEGF formalism for numerical computation [ABSTRACT FROM AUTHOR]

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

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

We present an approach based on local representation of frequency spectrum to calculate the surface contribution to thermodynamic properties of solids. The Green function theory of isolated point defects is discussed in detail which is also applicable to vibrations of surface atoms. The expression for local spectra of atoms is obtained in terms of the same site Green functions. The surface contribution to thermodynamic properties of solids is expressed in terms of the local frequency spectra of atoms in a few surface layers and the frequency spectrum of the infinite crystal satisfying the cyclic boundary condition. The usefulness of the formulation along with the ability of the recursion method to calculate local spectra without a recourse to detailed frequency calculations of slabs is emphasized. As an illustrative example, we present the surface contribution to low temperature lattice specific heat of tungsten due to (100) surface. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 with increasing the impurity potential is examined. It is shown that in the domain of the well-defined impurity resonance the local density of states at the first-nearest neighbor of the impurity site is approximately a scaled-up copy of the local density of states at the impurity site. The corresponding factor is found to be proportional to the squared impurity potential. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We compute the resonance energy transfer (RET) in a system composed of two quantum emitters near a host dielectric matrix in which metallic inclusions are inserted until the medium undergoes a dielectric-metal transition at percolation. We show that there is no peak in the RET rate at percolation, in contrast to what happens with the spontaneous emission rate of an emitter near the same critical medium. This result suggests that RET does not strongly correlate with the local density of states. [ABSTRACT FROM AUTHOR]

• Isotope engineering of near-field thermal diodes is explored for the first time. • Over 20% rectification enhancement is predicted for a wide parameter space. • At experimentally friendly gaps around 400 nm, 6-fold enhancement is possible. • Isotope-induced SPhP line shift and broadening are the key physical mechanisms. • Two guidelines for isotope engineering are proposed and supported with examples. Guided by a rational design approach centering on the electromagnetic local density of states (LDOS), we explore the potential of isotopically engineering radiative thermal diodes for enhanced rectification with a focus on the near field. Based on fluctuational electrodynamics, we theoretically demonstrate that for thermal diodes pairing thin films of intrinsic silicon (i -Si) and lithium hydride (LiX), the rectification ratio can increase by over six times with varying isotopic compositions. This is because by leveraging the isotope-induced shift and broadening of the surface phonon polaritons in LiX, more LDOS contrast provided by i -Si can be effectively converted into thermal rectification. Moreover, we show that such improvement is fairly robust, as evidenced by the prediction of over 20% rectification enhancement across a wide physical and geometric parameter space. Finally, inspired by insights from the i -Si-based thermal diodes, we propose general guidelines for implementing isotope engineering in the design of practical devices, which are further illustrated via representative diodes employing vanadium dioxide and silicon carbide as the active materials. Our work highlights the efficacy of isotopes in boosting the performance of radiative thermal diodes, which also holds promise for broader applications such as thermal transistors, thermal switches, and thermophotovoltaics. [ABSTRACT FROM AUTHOR]

Graphene nanoribbon (GNR) heterojunctions have been synthesized by a bottom-up approach on an Au (111) substrate from a mixture of two structurally similar but visually distinct chevron-type molecular precursors. The resulting heterojunctions were composed of the units of chevron GNRs (cGNRs) and new laterally extended chevron GNRs (eGNRs), which contained an additional benzene ring. Because of their intentional visual difference, cGNR and eGNR units could be conveniently distinguished in scanning tunneling microscopy images. Differential conductance (d I /d V ) mapping of GNR heterojunctions revealed differences in electronic structures of cGNRs and eGNRs. Interestingly, the characteristic conduction band states of cGNRs in the d I /d V maps were shown to be sensitive to the effects of both lateral extension of ribbons and the edge defects, emphasizing the importance of synthesizing GNRs and GNR heterojunctions with atomic precision. The d I /d V maps further showed that both effects could be localized within the corresponding GNR units even if they are bonded to structurally and electronically different neighbors, which suggests a possibility of engineering complex GNR-based electronic nanostructures with nanoscale modulation of properties. The new eGNR units could be potentially combined with other chevron-type GNRs, such as nitrogen-doped cGNRs, into a variety of new GNR heterojunctions. [ABSTRACT FROM AUTHOR]

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

Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and −2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms. [ABSTRACT FROM AUTHOR]

Using the first principles ground state method, the electronic properties of single Fe dopant in bulk and GaAs(1 1 0) surface are studied. Our calculations show that on-site correlations have significant effects on local geometrical and electronic structures for both bulk GaAs and GaAs(1 1 0) surface. Both t 2 g and e g orbitals of Fe impurity are split by on-site correlations and surface effects. Moreover, our calculated local density of states (LDOS), topography of in-gap states and valence band states based on DFT + U method agree well with experiments. Our calculated LDOS for Fe impurity on the GaAs(1 1 0) surface presents several electronic states above and below the Fermi level, and these states can be well interpreted with the hybridization between Fe 3d orbitals and p-like orbitals of host atoms. [ABSTRACT FROM AUTHOR]

We explore a model of armchair graphene nanoribbons tuned by functionalizing the edge states. Edge modifications are modeled by changing the electronic energy of the edge states in specific periodic patterns. The model can be considered to mimic a controlled doping process with different elements. The band structure, density of states, conductance, and local density of states are calculated, using the tight binding approach, Green's function methodology, and the Landauer formula. The results show interesting behaviors, which are considerably different from the properties of the perfect nanoribbons. The hybridization of conducting bands with non-conducting bands, which appear perfectly flat in the perfect ribbon, opens up and modifies gaps in conductance near the Fermi level. One particular pattern of edge functionalization causes a strong, symmetric, and systematic band gap change about the Fermi level, modifying the electronic characteristics in the energy dispersion, density of states, local density of states, and conductance. [ABSTRACT FROM AUTHOR]

We study the effect of mechanical deformations on the electronic properties of hexagonal flakes of bilayer graphENe. The behavior of electrons induced by triaxial strain can be described by an effective pseudo ‐ magnetic field which is homogENeous in the cENter of the flake. We find that in ‐ plane strain, applied to both layers equally, can break the layer symmetry leading to differENt behavior in the top and bottom layers of graphENe. At low ENergy, just one of the layers feels the pseudo ‐ magnetic field: the zero ‐ ENergy pseudo ‐ Landau level is missing in the second layer, thus creating a gap betweEN the lowest non ‐ zero levels. While the layer asymmetry is most significant at zero ENergy, interaction with the edges of the flake extENds the effect to higher pseudo ‐ Landau levels. The behavior of the top and bottom layers may be reversed by rotating the triaxial strain by 60°. (© 2015 WILEY ‐ VCH Verlag GmbH &Co. KGaA, Weinheim) Part of Focus Issue on ”Carbononics” (Eds.: Pawel Hawrylak, Francois Peeters, Klaus Ensslin) The influENce of mechanical deformations on the electronic properties of bilayer graphENe can be described by an effective pseudo ‐ magnetic field. The authors show that in ‐ plane triaxial strain, applied to both layers equally, can break the layer symmetry leading to differENt pseudo ‐ Landau level spectra in the top and bottom layers of graphENe. [ABSTRACT FROM AUTHOR]

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

The formation of a crystalline phase from the liquid is a nucleation-induced first order phase transformation, but one that cannot be monitored easily nor has it been comprehensively explained at the atomic level. In the context of heterogeneous nucleation, we have found that, during casting of Mg-base glass forming alloys inoculated with micron-sized yttria particles, crystalline Mg nucleates preferentially on a Cu buffer layer that initially forms on the surface of yttria particles. This partial transformation generated a unique bulk metallic glass/Mg flake composite structure at room temperature exhibiting an excellent combination of high strength and ductility. To understand this transformation at the atomic level, ab initio molecular dynamics simulations have been performed, the structures of the nucleated and nucleant particles have been analyzed and their orientation relationships have been compared with the experimental observations. Furthermore, the local electronic structure at the interface has been examined and the nature of chemical bonding assessed. It is revealed that while the strain generated in Mg structures formed onto the yttria substrate and the Cu buffer layer are comparable, the nucleation is promoted by the formation of chemical bonding between atomic constituents of the nucleus and nucleant and frustrated if such bonding fails to form. In addition, the works of separation for ordered Mg/Cu and ordered Mg/yttria interfaces obtained by applying density functional theory, are found to be consistent to the results of the local chemical bonding analysis. The outcomes of the simulations provide insight into the preferential nucleation of phases at inoculant particles in terms of the interfacial properties such as interfacial lattice mismatch and chemical bonding. [ABSTRACT FROM AUTHOR]

The dynamics of the inner surface of an infinitely long circular-cylindrical cavity in an isotropic elastic medium is studied in the whole range of the Poisson's ratio including negative values characteristic of auxetic materials. The existence of the unique long-lived propagation mode (true surface wave, TSW) has been confirmed on the clean surface with the following properties: (i) existence of a low frequency cut-off for all the azimuthal indices n except for n = 1 (flexural mode), (ii) polarization tending to that of the Rayleigh wave in the short wavelength limit, (iii) Airy phases (inflection points of dispersion curves) for n < 6 that shift towards short wave region when the Poisson's ratio becomes negative. A number of propagation modes with complex frequencies, i.e., with finite life times (surface leaky waves, pseudo surface waves) are found. The torsional leaky mode transforms into the skimming shear-horizontal wave (Love wave) in the short wavelength limit. An axial-radial leaky mode, similar to the Rayleigh wave but with reverse elliptical polarization turns out a physical solution except for extremely short wavelengths. A strong radial component of the longitudinal resonance occurs at wavelengths comparable to the cavity's radius especially in the incompressible limit. [ABSTRACT FROM AUTHOR]

Nanostructured materials offer the possibility to tailor light–matter interaction at scales below the wavelength. Metallic nanostructures benefit from the excitation of surface plasmons that permit light concentration at ultrasmall length scales and ultrafast time scales. The local density of states (LDOS) is a central concept that drives basic processes of light–matter interaction such as spontaneous emission, thermal emission and absorption. We introduce theoretically the concept of LDOS, emphasizing the specificities of plasmonics. We connect the LDOS to real observables in nanophotonics, and show how the concept can be generalized to account for spatial coherence. We describe recent methods developed to probe or map the LDOS in complex nanostructures ranging from nanoantennas to disordered metal surfaces, based on dynamic fluorescence measurements or on the detection of thermal radiation. [ABSTRACT FROM AUTHOR]

Recent advances in Au-thiolate nanocluster synthesis have allowed the total structural determination of several nanoclusters by X-ray crystallography. The high-precision structural information of these nanoclusters enables atomic site-specific analysis of local structure and electronic character. In this work, a site-specific comparative study of Au102(SR)44 and Au25(SR)18 was conducted to elucidate the size and site effects on the local environment and electronic character of their common surface structural unit, the -SR-Au-SR-Au-SR- 'double-staple' motif. Simulation of the pseudo-radial distribution function from extended X-ray absorption fine structure (EXAFS) shows a significant difference in their local environments despite their identical geometric shape. Local density of states ( l-DOS) calculations consistently reveal the difference in their electronic characters for gold d-electron density and d-DOS position. These differences are then related to the unique aurophilic interactions and size- or site-dependent electronic character of Au atoms in the double-staple motif. The differing local structure and electronic behaviour of the 'double-staple' motif in Au102(SR)44 and Au25(SR)18 highlight the significance of both size and site effects on the surface structure and electronic property of Au-thiolate nanoclusters. The theoretical results may also be useful in the interpretation of future experimental XAFS and X-ray photoelectron spectroscopy (XPS) data of these nanoclusters. [ABSTRACT FROM AUTHOR]

Based on a phenomenological model, we study theoretically the impurity effect in d-wave high-Tc superconductors in the presence of the charge-density-wave (CDW) order. Our results verify that the intensity of the resonance state induced by the impurity depends on the CDW scattering strength. It first increases and then decreases as the CDW scattering strength increases. Moreover, the impurity state exist only near the impurity site without the CDW modulation, while it would appear at quite far away from the impurity site in presence of the CDW modulation. The above results may be tested by later scanning tunneling microscopy experiments. [ABSTRACT FROM AUTHOR]

Abstract: For the first time the tunneling of Bloch waves through a contact of small diameter is studied in the framework of a model of an inhomogeneous tunnel δ-barrier of low transparency. The electron tunneling from bulk-mode states into the surface states localized near the contact interface is considered. An asymptotically exact expression (in the inverse height of the barrier) is derived for the conductance of the system. Prospects for the application of the obtained results to the theory of scanning tunneling microscopy are discussed. [Copyright &y& Elsevier]

Abstract: We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties. We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that such a heated probe above a surface performs a surface spectroscopy, in the sense that the spectrum of the heat current is closely related to the local electromagnetic density of states. The calculations agree well with available experimental data. [Copyright &y& Elsevier]

Local density of photonic states calculation based on multipole expansion method is a powerful tool for studying spontaneous emission and calculation of photon confinement in photonic crystal cavities. Using multipole expansion method, we calculate local density of states and quality factor of a two-dimensional three angle photonic crystal cavity. We also compare this quality factor result with the one calculated using finite difference time domain of a pulse response. It turns out that the local density of states calculation is more accurate and computationally less expensive. It is shown that shifting and changing the size of neighboring cylinders in the vicinity of photonic crystal cavity has a large impact on the mode volume and confinement. It is also described how the increasing of quality factor can be split up into local optimization of neighboring rods and the effect of increasing the number of photonic crystal layers, which exponentially increases the quality factor. This finding strongly suggests that the number of layers can be excluded from an optimization procedure. We also present structural design rules and geometrical freedom contour plots for the neighboring cylinders. These design rules can be used in further optimization of photonic crystal cavities. [ABSTRACT FROM AUTHOR]

The embedded atom method (EAM) potentials, with the universal form of the embedding function along with the Morse form of pair potential, have been employed to determine the potential parameters for three bcc transition metals: Fe, Mo, and W, by fitting to Cauchy pressure ( C − C)/2, shear constants $G_\textrm{v} =({C_{11} -C_{12} +3C_{44}})/5$ and C, cohesive energy and the vacancy formation energy. The obtained potential parameters are used to calculate the phonon dispersion spectra of these metals. Large discrepancies are found between the calculated results of phonon dispersion using the EAM and the experimental phonon dispersion results. Therefore, to overcome this inadequacy of the EAM model, we employ the modified embedded atom method (MEAM) in which a modified term along with the pair potential and embedding function is added in the total energy. The phonon dispersions calculated using potential parameters obtained from the MEAM show good agreement with experimental results compared to those obtained from the EAM. Using the calculated phonons, we evaluate the local density of states of the neighbours of vacancy using the Green's function method. The local frequency spectrum of first neighbours of vacancy in Mo shows an increase at higher frequencies and a shift towards the lower frequencies whereas in Fe and W, the frequency spectrum shows a small decrease towards higher frequency and small shift towards lower frequency. For the second neighbours of vacancy in all the three metals, the local frequency spectrum is not much different from that of the host atom. The local density of states of the neighbours of the vacancy has been used to calculate the mean square displacements and the formation entropy of vacancy. The calculated mean square displacements of the first neighbours of vacancy are found to be higher than that of the host atom, whereas it is lower for the second neighbours. The calculated results of the formation entropy of the vacancy compared well with other available results. [ABSTRACT FROM AUTHOR]

We perform the conventional band structure and local density of states (LDOS) calculations in the vicinity of the Fermi level at ab initio molecular orbital level with 6-31G base set for one DNA duplex with repeated mononucleotide sequences and four DNA duplexes with repeated dinucleotide sequences in B form neutralized by Na+. The LDOS of six other DNA duplexes with repeated trinucleotide sequences in the same states are analyzed. The obtained results are compared with those by the band calculations based on periodic boundary condition using screw axis symmetry. The investigations focused on the influence of the base composition and base sequence on the DNA conductivity. The band structure and LDOS calculation results indicated that base guanine is more important for DNA conductivity than the other bases, and DNA conductivity varies with base sequence of DNA. Moreover, poly (dG) • poly (dC) shows the best conductor in our DNA duplex models. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We introduced a procedure of using local density of states for increasing the quality factor and Purcell factor of photonic crystal cavities. We used multipole expansion method for accurate calculation of local density of photonic states, stationary field profile, Q-factor, mode volume and Purcell factor of photonic crystal cavities. We found out that the quality factor exponentially increases with the number of additional photonic crystal layers around the cavity while the mode frequencies stay unchanged. We also demonstrated the method in studying the defect mode's behavior in photonic crystal cavities and showed that high Q-factor, small mode volume and high Purcell factor could be obtained with optimization of geometrical parameters of first neighboring layer. [ABSTRACT FROM AUTHOR]

Electronic and spin transport properties of a benzene molecule connected to semi-infinite armchair and zigzag graphene nano-ribbon leads are calculated using non-equilibrium Green function (NEGF) method at zero bias regime. It is shown that, the molecule is conductive in a specific range of energy for both armchair and zigzag leads. This behavior is similar for both kinds of leads. In presence of Rashba spin-orbit interaction, the molecule shows spin filtering properties for both kinds of leads but these properties are not similar for armchair and zigzag leads. Also, a spin-polarized current is seen in the molecule connected to zigzag leads. The benzene molecule with Rashba spin-orbit interaction can be considered as an excellent candidate for molecular electronic and spintronic devices which can have very small dimensions relative to the conventional semiconductor devices. [ABSTRACT FROM AUTHOR]

The elongation method was developed to calculate the local density of states (LDOS) at ab initio molecular orbital (MO) level. This method is performed on eight types of DNA molecules: namely, a pitch of A- and B- type poly(dA)·poly(dT) and poly(dG)·poly(dC), and they are neutralized by H+ and Na+, respectively. The difference of total energy between elongation and conventional calculations in each step is considerably small in the order of 10−9 hartree/atom for 20 units of B-type poly(dA)·poly(dT) model. When the figures of total DOS of each model was compared, the energy gap of model containing Na+ is smaller than that of corresponding model containing H+. The LDOS for each model estimated by elongation method can well reproduce the results by conventional method. The LDOS figures show that the valence bands in A- and B-type DNA are formed by the highest occupied MOs (HOMOs) of adenine/guanine. Na+ can greatly decrease the energy of lowest unoccupied MO (LUMO) and consequently decrease the energy gap between LUMO and HOMO. The electron transfer between stacking adenine/guanine and sodium would play an important role in the conductivity of A- and B-type DNA. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]

The atomically resolved energy gap Δ( r) measured by Scanning Tunneling Microscopy has become a major challenge connecting to the nature of electronic states in cuprates superconductors. More recently, a two-energy-gap structure has been observed by many different experiments. We show that it is possible that the charge inhomogeneity gives rise to a potential barrier between the microscopic regions or grains that are the origin of these gaps. A larger Δ( r) is due to the single-particle bound states and the same potential gives rise to a smaller superconducting gap Δ( r). These results support the two-gap scenario and give a clear interpretation to the pseudogap phase. [ABSTRACT FROM AUTHOR]

Abstract: Based on the Bogoliubov de Gennes (BdG) equations, we study the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states for d-wave superconductor in anisotropic triangular system self-consistently with a strong magnetic field applied parallel to its conducting planes. We find that the two-dimensional FFLO state transforms to one-dimensional FFLO state as the system frustrated. The calculated local density of states are suggested to distinguish these states. [ABSTRACT FROM AUTHOR]

Abstract: A formal proof to relate the concept of electromagnetic local density of states (LDOS) to the electric and magnetic dyadic Green''s functions (DGF) is provided. The expression for LDOS is obtained by relating the electromagnetic energy density at any location in a medium at uniform temperature T to the electric and magnetic DGFs. The appropriate boundary conditions governing the DGFs are obtained and it is seen that the two types of DGFs are electromagnetic duals of each other. With this the concept of LDOS is also extended to material media. The LDOS is split into two terms—one that originates from the energy density in an infinite, homogeneous medium and the other that takes into account scattering from inhomogeneities. The second part can always be defined unambiguously, even in lossy materials. For lossy materials, the first part is finite only if spatial dispersion is taken into account. [Copyright &y& Elsevier]

Abstract: The quasiparticle scattering interference phenomenon characterized by the peaks in the local density of states is studied within the kinetic energy driven superconducting mechanism in the presence of a single impurity. By calculation of the Fourier transformed ratio of the local density of states at opposite energy, it is shown that the quasiparticle scattering interference phenomenon can be described qualitatively by a single impurity in the kinetic energy driven homogeneous d-wave superconducting state. The amplitude of the peak increases with increasing energy at the low energy, and reaches a maximum at the intermediate energy, then diminishes to zero at the high energy. The theory also predicts that with increasing doping, the position of the peak along the nodal direction moves towards to the center of the Brillouin zone, while the position of the peak along the antinodal direction is shifted to large momentum region. [Copyright &y& Elsevier]

The low-energy excitations of cuprate superconductors exhibit various characteristics that differ from those of simple Bogoliubov quasiparticles for pure $d_{x^{2}-y^{2}}$ -wave superconductors. Here, we report experimental studies of spatially resolved quasiparticle tunneling spectra of hole- and electron-type cuprate superconductors that manifest direct evidences for the presence of competing orders (COs) in the cuprates. In contrast to conventional type-II superconductors that exhibit enhanced local density of states (LDOS) peaking at zero energy near the center of field-induced vortices, the vortex-state LDOS of YBa2Cu3O7− δ (Y-123) and La0.1Sr0.9CuO2 (La-112) remains suppressed inside the vortex core, with pseudogap (PG)-like features at an energy larger (smaller) than the superconducting (SC) gap ΔSC in Y-123 (La-112). Energy histograms of the SC and PG features reveal steady spectral shifts from SC to PG with increasing magnetic field H. These findings may be explained by coexisting COs and SC: For hole-type cuprates with PG above Tc, the primary CO gap ( VCO) is larger than ΔSC and the corresponding COs are charge/pair-density waves with wave-vectors parallel to ( π,0)/(0, π). For electron-type cuprates without PG above Tc, VCO is smaller than ΔSC and the CO wave-vector is along ( π, π). This CO scenario may be extended to the ARPES data to consistently account for the presence (absence) of Fermi arcs in hole- (electron)-type cuprates. Fourier transformation of the vortex-state LDOS in Y-123 further reveals multiple sets of energy-independent wave-vectors due to field-enhanced pair- and spin-density waves. These results imply important interplay of SC with low-energy collective excitations. [ABSTRACT FROM AUTHOR]

Abstract: We study the possibility of charge ordered state in both single and bilayer graphene using a real space tight binding model. We argue that there is no charge ordered state in a single layer graphene. We also predict that the bilayer graphene can undergo a transition to a charge ordered state that is a commensurate CDW at low enough carrier density. We find that aside from the Coulomb interaction of the carriers of two layers that stabilizes the charge ordered state, so does the inter layer coupling. [Copyright &y& Elsevier]

Abstract: The local density of state (LDOS) has been studied by solving the mean-field Bogoliubov–de Gennes equations based on a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconducting orderings in the presence of a long-range Coulomb interaction. The vortex-core state with energies slightly above and below the Fermi level shows a four-fold symmetry with two-dimensional modulations under small on-site repulsion strength U, whereas it has a stripe structure for large U. The four-fold symmetry modulation with a periodicity of is recovered as a long-range Coulomb interaction has been included. Recent scanning-tunneling-microscopy experiments may be understood in terms of the present results. [Copyright &y& Elsevier]

Abstract: Based on the rigorous generalized Mie theory solution of Maxwell''s equations for dielectric cylinders we theoretically investigate the optical properties of two-dimensional deterministic structures based on the Fibonacci, Thue–Morse and Rudin–Shapiro aperiodic sequences. In particular, we investigate bandgap formation and mode localization properties in aperiodic photonic structures based on the accurate calculation of their local density of states (LDOS). In addition, we explore the potential of photonic structures based on aperiodic order for the engineering of radiative rates and emission patterns in erbium-doped silicon-rich nitride photonic structures. [Copyright &y& Elsevier]

A conference paper on how the honeycomb lattices of photonic crystals (PhC) affects the spontaneous emission of dipole is presented. It discusses the calculation of local density of states (LDOS) using plane-wave expansion method to determine the radiating behavior of the active medium embodied in PhC and to measure the electric field and magnetic field. It reveals that density of states (DOS) underrates the forbidden frequency regions; however, it overvalues the enhanced frequency regions.

Abstract: We measure local density of states (LDOS) for GaSb/InAs heterostructures with quantum wells in the valence band by scanning tunneling spectroscopy (STS) on the cleaved surface. Clear standingwave patterns of LDOS corresponding to the holes confined in the quantum wells are observed. [Copyright &y& Elsevier]

In order to study the design flexibility of photonic bandgap structures, we investigate different examples of 1D traditional Bragg layers and 2D photonic crystals. We have also considered a simple case of 3D woodpile structures. It turns out that in systems with large gaps, the evanescent waves penetrate into the bulk only distances comparable to one lattice constant. Therefore confinement of light can also be achieved without long range order, which leads to the introduction of novel photonic bandgap designs. Adhering to some constraints, the changes in the photonic bandgap in disordered structures are negligible. The important quantity to characterize the presence or absence of modes is the local photonic density of states, however bandgap phenomena in size and position disordered arrangements can also be verified with plane wave supercell calculations as well as finite difference time domain techniques. [ABSTRACT FROM AUTHOR]

We demonstrate that the dispersion of guided propagating modes in certain Photonic Crystal Waveguides (PCWGs) can be kept constant when the waveguide’s structure changes along the propagation direction. This suggests that the principle of constant group velocity matching may be utilized to improve impedance matching between different types of PCWGs while at the same time providing significant design flexibility. We illustrate this principle through the design of several efficient coupling structures between two different PCWGs via a local density of states and Fourier transform analysis of the associate electromagnetic fields. The couplers consist of heterostructures whose individual sections exhibit rather distinct structural parameters. Furthermore, we compare these structures to an adiabatic coupler. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical study of the low temperature lattice specific heat of Au0.96Cd0.04 and Ag0.96Al0.04 dilute alloys has been carried out. Lattice Green''s function method has been used to calculate the local density of states of substitutional impurity and change in lattice specific heat in these alloys. The condition of resonance and localized modes has also been investigated for possible occurrence of these modes. The calculated results of change in specific heat are compared with the experimental measurements and a good agreement between theory and experiment has been obtained. Although, the calculated results did not show any resonance modes, localized modes above the maximum frequency have been obtained. The change in lattice specific heat as a result of introduction of small fraction of impurities is explained on the basis of obtained localized modes. [Copyright &y& Elsevier]

Abstract: We numerically study the vortex core structure in a noncentrosymmetric superconductor such as CePt3Si without mirror symmetry about the xy plane. A single vortex along the z axis and a mixed singlet–triplet Cooper pairing model are considered. The spatial profiles of the pair potential, local density of states, supercurrent density, and radially-textured magnetic moment density around the vortex are obtained in the clean limit on the basis of the quasiclassical theory of superconductivity. [Copyright &y& Elsevier]

Abstract: Scanning tunneling spectroscopy (STS) based on scanning tunneling microscopy (STM) makes it possible to map the local electronic density of states for clean surfaces and for those with adsorbates. We have developed a protocol that allows us to obtain the spectral fingerprints of halogen atoms on Si(001), and we use those fingerprints to distinguish between adatom species for surfaces with Cl and Br mixed adsorbates. The key to the process is the energy distribution of the antibonding states that depend on the halogen species. [Copyright &y& Elsevier]

Abstract: Scanning tunneling microscopy (STM) was used to study the surface structures of dry-prepared and di-chloroethane-treated HOPG samples. Both triangular and honeycomb structures were simultaneously observed with the same tip at room temperature around a strand (grain boundary) on the HOPG surface. This observation did not support the tip effect in STM imaging explanation for HOPG in literature. A general layer-sliding model was utilized to explain the experimental results: sliding of the HOPG topmost layer was used to explain the origins of the triangular and honeycomb structures, and molecule intercalation into inter-layer spacing between the first and second layers of HOPG induced inhomogeneous deformation of the HOPG topmost layer that accordingly generated the Moiré patterns of the HOPG sample in di-chloroethane. [Copyright &y& Elsevier]

Abstract: The electronic structure around an impurity in spin triplet p-wave superconductors is investigated by the Bogoliubov–de Gennes theory on a tight-binding model. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between -wave and -wave superconducting states. [Copyright &y& Elsevier]