Showing papers on "Fermi energy published in 1996"
TL;DR: In this article, the electronic density of states in a non-superconducting wire in good contact with a superconductor, at distances of 200, 300 and 800 nm from the interface, was measured by tunneling spectroscopy.
Abstract: We have measured by tunneling spectroscopy the electronic density of states in a non-superconducting wire in good contact with a superconductor, at distances of 200, 300 and 800 nm from the interface. Closest to the interface, the density of states near the Fermi energy is reduced to 55% of its normal value. At the farthest measurement point, this dip has nearly completely disappeared. We compare our data to predictions based on the Usadel equations.
169 citations
TL;DR: The rapid decay of spin alignment over small changes to both higher and lower magnetic field provides experimental evidence for the presence of Skyrmion excitations where exchange energy dominates Zeeman energy in the quantum Hall regime at 0ex-0ex=1.
Abstract: A dramatic reduction in the spin polarization of a two-dimensional electron gas in a magnetic field is observed when the Fermi energy moves off the midpoint of the spin gap of the lowest Landau level, $\ensuremath{
u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$. The spin polarization is measured by magnetoabsorption spectroscopy which distinguishes the occupancy of the two electron spin states. The rapid decay of spin alignment over small changes to both higher and lower magnetic field provides experimental evidence for the presence of Skyrmion excitations where exchange energy dominates Zeeman energy in the quantum Hall regime at $\ensuremath{
u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$.
144 citations
TL;DR: In this article, the structural and electronic properties of divalent hexaborides like SrB6, CaB6 and of ferromagnetic EuB6 were calculated using the full-potential linearized augmented plane wave (FLAPW) method, within the local (spin) density approximation.
Abstract: Recent experiments suggest that divalent hexaborides like SrB6 and CaB6, traditionally considered small-gap semiconductors, can actually be semimetals. We calculate the structural and electronic properties of SrB6, CaB6 and of ferromagnetic EuB6, using the full-potential linearized augmented plane wave (FLAPW) method, within the local (spin) density approximation. The lattice constants and internal parameters are in very good agreement with the measured ones. Because of a small band overlap at the X point, all the materials are semimetals. The calculated Hall coefficient for SrB6 changes sign around zero doping, and has the freeelectron value for doping beyond ≈ 1.5%. The plasma frequency has a minimum at zero doping. We interpret the high-temperature transport properties of SrB6 and CaB6 in terms of a thermal gap deduced from the shape of the density of states around the Fermi energy. We also calculate the imaginary part of the dielectric function for SrB6, which can be compared to recent experiments.
144 citations
TL;DR: In this paper, the authors give a complete review of various expansions which may be used for quick and accurate computing of the thermodynamic functions of an ideal Fermi gas and show how to find an analytic form of the equation of state which is valid for a moderate degree of relativism of fermions.
Abstract: We give a complete review of various expansions which may be used for quick and accurate computing of the thermodynamic functions of an ideal Fermi gas. We begin with the well-known expression for the equation of state of an ultrarelativistic Fermi gas, which is in thermal equilibrium with blackbody radiation. This elementary expression is valid when the fermion mass is completely neglected in comparison to the average fermion kinetic energy. After that we show how to take into account the fermion mass; in other words, how to find an analytic form of the equation of state which is valid for a moderate degree of relativism of fermions. Contrary to the known expressions, the obtained expansion over the mass powers, as well as the elementary equation of state of an ultrarelativistic gas, holds for both a cold degenerate and a hot nondegenerate gas. Then we present expressions efficient in various ranges of temperature and density and derive some new approximations. The boundaries of applicability of all the expansions are specified on the temperature-density plane. {copyright} {ital 1996 The American Astronomical Society.}
124 citations
TL;DR: Self-consistent calculations of the electronic structure of quantum wires with an in-plane magnetic field parallel to the wire using the spin-polarized density-functional theory of Kohn and Sham show that exchange interactions cause a large subband splitting whenever the Fermi energy passes the subband threshold energies.
Abstract: We report on self-consistent calculations of the electronic structure of quantum wires with an in-plane magnetic field parallel to the wire. The spin-polarized density-functional theory of Kohn and Sham is used. The self-consistent results show that exchange interactions cause a large subband splitting whenever the Fermi energy passes the subband threshold energies. Full spin polarization appears at low electron densities. The results are consistent with recent observations of a conductance anomaly in a quantum point contact and its interpretation in terms of spontaneous spin polarization of the lowest subband. On the basis of the present model we conjecture that similar conductance anomalies may appear also in the higher subbands at zero magnetic field. Finite magnetic fields tend to suppress the spin polarization induced by exchange interactions. A diamagnetic shift of the subbands is determined and is in qualitative agreement with observations. \textcopyright{} 1996 The American Physical Society.
112 citations
TL;DR: In this paper, a Raman scattering experiment on metallic La0.7Sr0.3MnO3 has been carried out using different excitation wavelengths as a function of temperature from 15 K to 300 K.
Abstract: Raman scattering experiments on metallic La0.7Sr0.3MnO3 have been carried out using different excitation wavelengths as a function of temperature from 15 K to 300 K. Our data suggest a Raman mode attributed to electronic excitations centered at 2100 cm-1 whose intensity decreases with increasing temperature. If the Raman mode is attributed to single-particle excitation associated with the fluctuations of the mass tensor, the decreased intensity would then imply a reduction in the density of states at the Fermi energy with increasing temperature.
91 citations
TL;DR: The DOS differs from the linear muffin tin orbital calculated DOS and the possible roles of electron scattering and inhomogeneous electronic structure close to the surface are discussed.
Abstract: Tunneling spectroscopy studies on oxidized and bare surfaces of icosahedral {ital i}-AlPdRe, {ital i}-AlCuFe, and approximant {alpha}-AlMnSi phases reveal specific features of the density of states (DOS) close to the Fermi level as compared to the crystalline nonapproximant {omega}-AlCuFe phase. The Fermi energy lies in the middle of a narrow pseudogap of about 50meV width. For higher energies, the DOS exhibits a square root energy dependence attributed to electron-electron interaction effects. The DOS differs from the linear muffin tin orbital calculated DOS and the possible roles of electron scattering and inhomogeneous electronic structure close to the surface are discussed. {copyright} {ital 1996 The American Physical Society.}
74 citations
TL;DR: The role of multiple layers in the high-temperature superconductors continues to be one of the most intriguing puzzles, with many conflicting proposals and interpretations as mentioned in this paper, and one proposal is that superconductivity is enhanced by electronic correlations which are argued to greatly reduce single-particle hopping between layers while allowing pair-tunneling.
Abstract: The role of multiple layers in the high-temperature superconductors continues to be one of the most intriguing puzzles, with many conflicting proposals and interpretations. One proposal is that superconductivity is enhanced by electronic correlations which are argued to greatly reduce single-particle hopping between layers while allowing pair-tunneling [1]. Angle-resolved photoemission (ARPES) studies [2,3] of the energy spectrum near the Fermi energy for bi-layer materials can in principle answer the questions of the nature of the bonding and antibonding bands near the Fermi level. However, one recent ARPES experiment [3] resolved only one CuO2 band at the Fermi surface in BSCO-2212, supporting the idea of a greatly reduced interlayer hopping, whereas another measurement [2] reports two Fermi sheets, in general agreement with the predictions of band structure calculations. In addition, there is evidence for important effects of coupling between the layers in bilayer systems. Neutron scattering experiments see maximum intensity for spin scattering for wave vectors the qz ∼ π/L, where L is the interlayer spacing, for both the antiferromagnetic insulator and in the superconductor [4]. A generic feature which has emerged from the ARPES experiments [2,3] is a “flat-band” or “extended van-Hove singularity” which is “pinned” to the Fermi level for different hole dopings. Bifurcated saddle points very close to the Fermi level had, in fact, been predicted by LDA calculations for YBCO-123 [5] and caused by dimpling of the CuO2 planes [6]. The flat band observed by ARPES has also been attributed to many-body effects [7–9], and a number of studies have been done for correlated electronic states in a single CuO2 plane. The flat region in the quasiparticle spectrum has been proposed to be a “fermion condensate” [10,11], or a non-Fermi liquid area formed in (q, ω) space near two-dimensional van-Hove singularity [12]. The one-band [7,9] and three-band [13] Hubbard models as well as t-J model [8] show a flat quasiparticle band just below the Fermi energy, which has an “extended” van-Hove singularity near the X(π,0)-point, due to antiferromagnetic spin fluctuations. The same antiferromagnetic fluctuations at q ≈ (π, π) lead to dx2−y2 superconductivity [14] with a relatively high transition temperature. For the two-plane Hubbard model [15,16] with a simple tight-binding spectrum a reduction of superconducting correlations was found due to the interlayer coupling. In this paper we study the bi-layer Hubbard model with realistic LDA derived hopping integrals. Combination of this realistic tight-binding (TB) model with many-body effects accounts for anomalous properties of cuprate superconductors. Thus in the normal state of our BSCO model, many body effects strongly reduce the splitting between the bonding and antibonding bands in the regions in the k-space where the one-body splitting is large, leading to flat bands near the chemical potential to within an energy of order room temperature. On the other hand, in the regions where the many-body effects are small, there is also little splitting in the one-particle spectrum, due to geometry of the bi-layer bonding in the cuprates. We analyze the pinning of the chemical potential to these van-Hove singularities in the case of a mono- and bi-layer model for different hole dopings. A calculation of the superconducting transition temperature shows robust stability of the dx2−y2 state in the “three-dimensional” bi-layer case. Let us start with the Hubbard hamiltonian for a bilayer CuO2 model:
69 citations
TL;DR: Close to particle-hole symmetry, the Kondo effect is suppressed for the cases of greatest relevance (r=1 and 2), but away from this symmetry, any quenching of the impurity moment is accompanied by a low-temperature decrease in the impurities resistivity, rather than the increase found in metals.
Abstract: In a number of systems, including certain semiconductors and unconventional superconductors, the effective density of states varies like |E-${\mathit{E}}_{\mathit{F}}$${\mathrm{|}}^{\mathit{r}}$ near the Fermi energy. The behavior of dilute magnetic impurities in such systems is studied using a nonperturbative renormalization-group approach. Close to particle-hole symmetry, the Kondo effect is suppressed for the cases of greatest relevance (r=1 and 2). Away from this symmetry, any quenching of the impurity moment is accompanied by a low-temperature decrease in the impurity resistivity, rather than the increase found in metals. \textcopyright{} 1996 The American Physical Society.
62 citations
TL;DR: The role of numerous virtual transitions, “vibrational superexchange,” in global transport is examined both for typical pa the state space and special states often interrogated experimentally.
Abstract: Criteria for ergodicity and rates of energy flow in a quantum mechanical system of N coupled anharmonic oscillators where N is large are determined at energies near the ground state of system. High-order resonances are important for the transition at large N . The role of numerous virtual transitions, “vibrational superexchange,” in global transport is examined both for typical pa the state space and special states often interrogated experimentally.
55 citations
TL;DR: It is found that the susceptibility enhancement factor ~with respect to the Fermi gas of the same density! reaches values larger than in bulk liquid 3 He in high-areal-density fluids.
Abstract: We present results on the magnetic susceptibility of the second atomic layer fluid of 3 He adsorbed on graphite over a large temperature and coverage range. The fluid is found to display the well characterized behavior of a Fermi liquid. The temperature dependence of the magnetic susceptibility can be described well by Dyugaev’s phenomenological theory of Fermi liquids. The effective Fermi temperature has been determined as a function of coverage. We find that the susceptibility enhancement factor ~with respect to the Fermi gas of the same density! reaches values larger than in bulk liquid 3 He in high-areal-density fluids. In this regime the films constitute experimental model systems for the theory of strongly correlated fermions. Using previous heat-capacity measurements performed on the same system allows a direct comparison with the predictions of the quasilocalized model and the paramagnon model.
TL;DR: In this article, the electronic structures of dangling-bond wires on an H-terminated Si(100)2/ifmmode/times\else\texttimes\fi{}1 surface have been examined by using first-principles calculations within the local density functional approach.
Abstract: Electronic structures of several atomic wires on an H-terminated Si(100)2\ifmmode\times\else\texttimes\fi{}1 surface have been examined by using first-principles calculations within the local-density-functional approach. Several dangling-bond (DB) wires, which are constructed by extracting H atoms from the surface, have been examined and found to have different characteristics depending on their structures. Electronic states near the Fermi energy are localized around the wire on the atomic scale in DB wires along the dimer rows on the surface, while they are much more delocalized around a DB wire in the direction across the dimer rows. Ga adsorbate atomic wires, which are formed by Ga adsorbates around the above wires, have also been examined. Several metastable geometries of Ga adsorbates were found. It was found that formation of Ga dimers was stable on this surface.
TL;DR: It is shown that at high densities it is also possible to relate the transport equations to the zero-curvature condition of a Chern-Simons theory in three dimensions, even when quarks are not considered ultrarelativistic.
Abstract: Classical transport theory is used to study the response of a non-Abelian plasma at zero temperature and high chemical potential to weak color electromagnetic fields. In this article the parallelism between the transport phenomena occurring in a non-Abelian plasma at high temperature and high density is stressed. In particular, it is shown that at high densities it is also possible to relate the transport equations to the zero-curvature condition of a Chern-Simons theory in three dimensions, even when quarks are not considered ultrarelativistic. The induced color current in the cold plasma can be expressed as an average over angles, which represent the directions of the velocity vectors of quarks having Fermi energy. From this color current it is possible to compute $n$-point gluonic amplitudes, with arbitrary $n$. It is argued that these amplitudes are the same as the ones computed in the high chemical potential limit of QCD, which are then called hard dense loops. The agreement between the two different formalisms is checked by computing the polarization tensor of QED due to finite density effects in the high density limit.
TL;DR: In this paper, the authors derived and evaluated expressions for the dc tunneling conductance between interacting two-dimensional electron systems at nonzero temperature and derived the finite electronic lifetime produced by electron-electron interactions as a function of temperature for quasiparticles near the Fermi circle.
Abstract: We derive and evaluate expressions for the dc tunneling conductance between interacting two-dimensional electron systems at nonzero temperature. The possibility of using the dependence of the tunneling conductance on voltage and temperature to determine the temperature-dependent electron-electron scattering rate at the Fermi energy is discussed. The finite electronic lifetime produced by electron-electron interactions is calculated as a function of temperature for quasiparticles near the Fermi circle. Vertex corrections to the random-phase approximation substantially increase the electronic scattering rate. Our results are in an excellent quantitative agreement with experiment. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the authors present an extensive work on the conductance as well as the transmission and reflection probabilities of disordered nanowires, using a tight binding Hamiltonian with diagonal disorder to describe the quantum wire, and a two-terminal Landauer-type formula for its conductance.
Abstract: We present an extensive work on the conductance as well as the transmission and reflection probabilities of disordered nanowires. We use a tight-binding Hamiltonian with diagonal disorder to describe the quantum wire, and a two-terminal Landauer-type formula for its conductance. For short wires, in the quasiballistic regime, we study the behavior of these quantities as a function of the degree of disorder and the Fermi energy of the electron, following their evolution when a channel disappears, finding an effective closing of the last opened channel (for strong disorder) before the actual closing energy. We analyze the influence of the length and width of the wire, noticing different transmission and reflection behavior depending on the incident channel. We have compared these results with the isotropic model predictions and found that these are satisfied only partially. \textcopyright{} 1996 The American Physical Society.
TL;DR: The results suggest that the effect of strain on the anisotropy energy is strongly correlated with the type of atomic species adjacent to the Co layer and cannot be determined solely from the value of strain introduced in theCo layer.
Abstract: First-principles calculations of the magnetic anisotropy energies of Pd/Co metallic multilayers have been performed to investigate the effect of strain on the interface magnetic anisotropy. Also, to clarify the contribution of the interface to anisotropy, the anisotropy energies of an unsupported Co monolayer and bulk Co have been calculated. These two systems have different interfaces compared to the Pd/Co multilayer in the sense that an unsupported Co monolayer and bulk Co can be considered as vacuum/Co and Co/Co multilayers, respectively. A Pd/Co multilayer is predicted to exhibit a perpendicular magnetic anisotropy in accordance with experiment. Bulk Co shows perpendicular anisotropy, but the anisotropy energy is quite small compared to that of Pd/Co. On the contrary, an unsupported Co monolayer shows an in-plane anisotropy. These differences suggest the importance of the existence of the interface for perpendicular magnetic anisotropy, which originates from the modification of the local electronic structure of a Co layer due to the presence of the interface. The strength of the hybridization of electronic states at the interface determines the relative position of the Fermi energy to the position of the local density of states (LDOS) of |m|=2 character of Co d electrons of minority spin. If the LDOS of |m|=2 character is large at the Fermi energy, the system shows a perpendicular anisotropy. As for the effect of strain, the anisotropy energy of Pd/Co increases as a function of interatomic distance in the in-plane direction, while that of a Co monolayer decreases. Compared to these two systems, the magnetoelastic constant of bulk Co is considerably smaller. These results suggest that the effect of strain on the anisotropy energy is strongly correlated with the type of atomic species adjacent to the Co layer and cannot be determined solely from the value of strain introduced in the Co layer. In the case of a heterointerface, the strength of hybridization between the orbitals inside the monolayer and that between the orbitals in adjacent monolayers are quite different and this fact leads to the large strain dependence of the anisotropy. \textcopyright{} 1996 The American Physical Society.
TL;DR: It is shown that a constant initial energy, angle-scanned (CIE-AS) photoemission spectrum for emission from the Fermi energy containsFermi surface (FS) signatures which originate from density of states type {ital indirect} transitions.
Abstract: We show that a constant initial energy, angle-scanned (CIE-AS) photoemission spectrum for emission from the Fermi energy ({ital E}{sub {ital F}}) contains Fermi surface (FS) signatures which originate from density of states type {ital indirect} transitions. Such previously unrecognized FS features in a CIE-AS spectrum would provide a robust and straightforward means of determining Fermi surfaces. Furthermore, the associated photointensity should yield a new window on {ital k}{sub {perpendicular}} dispersion related issues in materials. Extensive simulations of CIE-AS spectra from low index faces of Cu are presented within the framework of the one-step photoemission model in order to delineate the nature of these new spectral features. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this paper, the magnetic anisotropic energies of X/Co (X=Pt, Cu, Ag and Au) metallic multilayers have been investigated to investigate the effect of strain on the magneto-elastic constants.
Abstract: A first‐principles calculation of the magnetic anisotropy energies of X/Co (X=Pt, Cu, Ag and Au) metallic multilayers has been performed to investigate the effect of strain on the magnetic anisotropy. It is successfully predicted that Pt/Co and Au/Co multilayers exhibit perpendicular magnetic anisotropies in accordance with experiments. The strength of the hybridization of electronic states at the interface determines the relative position of the Fermi energy to the local density of states (LDOS) of ‖m‖=2 character of Co d electrons of minority spin. If the LDOS of ‖m‖=2 character is large at the Fermi energy, a system shows a perpendicular anisotropy. The anisotropy energies of all the systems increase as a function of interatomic distance in the in‐plane direction. The magneto‐elastic constants are more than twice the value of pure Co. The origin of this large value is explained in terms of the change of relative position of the Fermi level to that of the LDOS of ‖m‖=2 character as the value of strain i...
TL;DR: The energy band structure of an antidot array defined in a strip geometry of finite width is calculated as a function of the magnetic field, in a parameter range typical of existing experiments, and with edge aspects explicitly taken into account.
Abstract: The energy band structure of an antidot array defined in a strip geometry of finite width is calculated as a function of the magnetic field, in a parameter range typical of existing experiments, and with edge aspects explicitly taken into account. The calculations are based on a hybrid recursive Green-function technique specially adapted to problems of this type. The current densities associated with representative Bloch states are calculated and visualized. At a given Fermi energy and in zero magnetic field, the set of propagating Bloch states consists of fast states with essentially one-dimensional laminar type flow , channeling between rows of antidots, and slower ones with a genuinely two-dimensional flow of vortex character. Simple physical arguments are used to explain the existence of the different types of states. At low magnetic fields much of the character of the zero-field states is retained. At magnetic fields sufficiently high that the classical cyclotron diameter is close to the lattice constant of the array, the magnetobands correspond to edge states and to states of the ‘‘runaway’’ type, in which electrons bounce off antidots in consecutive unit cells. Surprisingly, states corresponding to electrons in classical orbits pinned around single antidots play only a minor role. With a further increase of the magnetic field, essentially only edge states survive. In this high-field regime, states beyond the edge states only exist in narrow energy bands, and these states correspond to bulk transport with electrons hopping between quasilocalized states.
TL;DR: In this paper, measurements in a perpendicular magnetic field of the frictional drag between two closely spaced, but electrically isolated, two-dimensional electron gases have been performed, showing that when the Fermi energy lies at the centre of a Landau level, the drag can be enhanced by two orders of magnitude over the zero field signal.
Abstract: We present measurements in a perpendicular magnetic field of the frictional drag between two closely spaced, but electrically isolated, two-dimensional electron gases. At high temperatures, when the Landau level structure is smeared out, the transresistivity shows a magnetic field dependence and an approximately linear temperature dependence. As the temperature is lowered below 20 K, the transresistivity shows structure reflecting the formation of Landau levels and, in general, the drag is more sensitive to the spin splitting of the Landau levels than the Shubnikov - de Haas oscillations. When the Fermi energy lies at the centre of a Landau level, the drag can be enhanced by two orders of magnitude over the zero field signal. In contrast, when lies between Landau levels in the quantum Hall regime, the drag signal tends to zero. We have also measured the transverse voltage in the drag layer and find no evidence for a Hall transresistance.
TL;DR: In this paper, the results of a study of quantum oscillations in the layered perovskite superconductor Sr 2 RuO 4 have been reported, and three predicted sheets of the Fermi surface have been observed.
Abstract: We report the results of a study of quantum oscillations in the layered perovskite superconductor Sr 2 RuO 4 . All three predicted sheets of the Fermi surface have been observed, and we show how the measured Fermi surface parameters and quasiparticle cyclotron masses can be used to make successful quantitative predictions of a number of physical properties that can be measured independently.
30 Oct 1996-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the band gaps and electronic structures of doped and undoped icosahedra are reported and the occupied and unoccupied electronic structure of icosahedral closo-1,2-dicarbadodecarborane (C2B10H12) thin films are described.
Abstract: The band gaps and electronic structures of doped and undoped films of molecular icosahedra are reported. The occupied and unoccupied electronic structure of undoped icosahedral closo-1,2-dicarbadodecarborane (C2B10H12) thin films resembles that of the isolated molecule. The Fermi level of the molecular thin films is roughly at midgap. Upon initial Na doping of the orthocarborane films, an unoccupied extramolecular (exopolyhedral) state forms within the gap at an energy of about 3 eV above the Fermi energy. With Na doping, the film of molecular icosahedra resembles a system with Hubbard-like bands and an appreciable correlation U.
TL;DR: By averaging over an ensemble of many individual members of an ensemble, the energy-averaged weak-localization effect for each cavity shape is obtained and the average result does display the expected minimum at B50.
Abstract: We have fabricated ballistic cavities from a two-dimensional GaAs electron gas in which the Fermi energy can be varied independent of cavity shape. For each cavity, we have measured the magnetoconductance $G(B)$ of many individual members of an ensemble, with each member labeled by its Fermi energy. We find that $G(B)$ of a single ensemble member does not always display the minimum at $B=0$ which is the signature of weak localization. By averaging over our ensemble, we have obtained the energy-averaged weak-localization effect for each cavity shape. The average result does display the expected minimum at $B=0$. We compare our results with recent analytical theories and numerical simulations of weak localization in cavities with chaotic classical scattering and find good quantitative agreement.
TL;DR: In this paper, local probe tunneling spectroscopy of Bi2Sr2CaCu2O8+δ single crystals for different oxygen concentrations, from optimally doped (Tc=92.2 K) to highly overdoped (tc=56.0 K) phases, was presented.
Abstract: We present local probe tunneling spectroscopy of Bi2Sr2CaCu2O8+δ single crystals for different oxygen concentrations, from optimally doped (Tc=92.2 K) to highly overdoped (Tc=56.0 K) phases. With increasing oxygen overdoping, the superconducting gap (Δp) is reduced and the dip structure beyond Δp at negative sample bias1 shifts toward the Fermi energy. Apart from the shift in energy of these features, the generic shape of the tunneling spectra remains unchanged. The gap roughly scales with Tc, and 2Δp/kBTc stays large even in the highly overdoped phase. We also present preliminary results on the temperature dependence of the tunneling spectra. They are consistent with a gap that is largely independent on temperature up to the vicinity of Tc
TL;DR: In this article, the low-temperature AC conductance of a one-dimensional electron system with a strong interaction of finite range is calculated by using linear response theory, where the conductance factorizes into parts which depend on the internal properties of the system, and the external probe.
Abstract: The low-temperature AC conductance of a one-dimensional electron system with a strong interaction of finite range is calculated by using linear response theory. The conductance factorizes into parts which depend on the internal properties of the system, and the external probe. For short-range interaction, the result resembles that for non-interacting electrons, but with the zero-frequency limit and the Fermi velocity renormalized by the interaction strength. For strong and long-range interaction, the conductance shows a peak that is related to charge-wave excitations. In this limit, the AC conductance can be simulated by a quantum capacitance and a quantum inductance.
TL;DR: In this paper, a real-space Green-function technique is used in a single-band tight-binding model to evaluate the Ohmic resistivities and the giant magnetoresistance in trilayer systems.
Abstract: A real-space Green-function technique, in which the scattering is treated exactly, is used in a single-band tight-binding model to evaluate the Ohmic resistivities and the giant magnetoresistance in trilayer systems. The model includes (i) spin dependence of the density of states and Fermi velocity in the magnetic material, giving a qualitative representation of Co/Cu and Fe/Cr systems; (ii) spin-independent bulk disorder, representing intrinsic defects in real systems; (iii) chemically sharp interfacial roughness. It is found that for parameters that produce realistic total resistivities, the spin-polarized band structure in conjunction with the spin-independent bulk disorder gives the main contribution to the giant magnetoresistance. The chemically sharp interfacial roughness enhances the effect. Its contribution becomes significant in the limit of sufficiently dense roughness steps, sufficiently weak bulk disorder, and sufficiently thin magnetic layers.
TL;DR: By analyzing the occupation of the energy levels at the Fermi energy as a function of cluster size, it is shown how the shell and supershell structures for a given density arise from the specific arrangement of energy levels.
Abstract: We present the results of self-consistent calculations of the electronic shell and supershell structures for clusters having up to 6000 valence electrons. The ionic background is described in terms of a homogeneous jellium. The calculations were performed for a series of different electron densities, resembling Cs, Rb, K, Na, Li, Au, Cu, Tl, In, Ga, and Al, respectively. By analyzing the occupation of the energy levels at the Fermi energy as a function of cluster size, we show how the shell and supershell structures for a given density arise from the specific arrangement of energy levels. We investigate the electronic shells and supershells obtained for different electron densities. Using a scaling argument, we find a surprisingly simple dependence of the position of the supernodes on the electron density. {copyright} {ital 1996 The American Physical Society.}
TL;DR: Renormalization-group methods are applied to the Anderson model for a localized level coupled to a Fermi system in which the density of states varies like r, thereby narrowing the range of parameters within which the impurity spin becomes Kondo screened.
Abstract: Renormalization-group methods are applied to the Anderson model for a localized level coupled to a Fermi system in which the density of states varies like ${|\ensuremath{\epsilon}|}^{r}$ near the Fermi energy ($\ensuremath{\epsilon}=0$). This model with $r=1 or 2$ may describe magnetic impurities in unconventional superconductors and certain semiconductors. The pseudogap suppresses mixed valence in favor of local-moment behavior. However, it also reduces the exchange coupling on entry to the local-moment regime, thereby narrowing the range of parameters within which the impurity spin becomes Kondo screened.
TL;DR: The Integer Quantum Hall Effect (IQHE) is investigated using an inductive method and conclusions can be derived that the extended states located at the bulk of the sample below the Fermi energy are capable of carrying a substantial amount of Hall current, but cannot screen an external electrostatic potential.
Abstract: We investigated the integer quantum Hall effect (IQHE) using an inductive method. The following conclusions can be derived from our study: (i) When the Fermi energy is located between Landau levels the only extended states at the Fermi energy are located at the physical edges of the sample. (ii) The extended states located at the bulk of the sample below the Fermi energy are capable of carrying a substantial amount of Hall current, but cannot screen an external electrostatic potential.