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Articles 1 - 17 of 17
Full-Text Articles in Physics
A Novel Direct Method Of Fermi Surface Determination Using Constant Initial Energy Angle-Scanned Photoemission Spectroscopy, M. Lindroos, A. Bansil
A Novel Direct Method Of Fermi Surface Determination Using Constant Initial Energy Angle-Scanned Photoemission Spectroscopy, M. Lindroos, A. Bansil
Arun Bansil
We show that a constant initial energy, angle-scanned (CIE-AS) photoemission spectrum for emission from the Fermi energy (EF) contains Fermi surface (FS) signatures which originate from density of states type 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 k⊥, 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.
X-Ray Absorption Near-Edge Spectra Of Overdoped La₂₋ₓsrₓcuo₄ High-T(C) Superconductors, Towfiq Ahmed, Tanmoy Das, J. Kas, B. Barbiellini, Fernando Vila, R. Markiewicz, A. Bansil, J. Rehr
X-Ray Absorption Near-Edge Spectra Of Overdoped La₂₋ₓsrₓcuo₄ High-T(C) Superconductors, Towfiq Ahmed, Tanmoy Das, J. Kas, B. Barbiellini, Fernando Vila, R. Markiewicz, A. Bansil, J. Rehr
Arun Bansil
We present results for realistic modeling of the x-ray absorption near edge structure (XANES) of the overdoped high-Tc superconductor La₂₋ₓSrₓCuO₄ in the hole doping range x = 0.20 - 0.30. Our computations are based on a real-space Green's function approach in which strong-correlation effects are taken into account in terms of a doping-dependent self-energy. The predicted O K-edge XANES is found to be in good accord with the corresponding experimental results in this overdoped regime. We find that the low energy spectra are dominated by the contribution of O atoms in the cuprate planes, with little contribution from apical O …
Angle-Resolved Photoemission-Study Of (100), (110), And (111) Surfaces Of Cu0.9a10.1: Bulk And Surface Electronic-Structure Of The Alloy, H. Asonen, M. Lindroos, M. Pessa, P. Prasad, R. Rao, A. Bansil
Angle-Resolved Photoemission-Study Of (100), (110), And (111) Surfaces Of Cu0.9a10.1: Bulk And Surface Electronic-Structure Of The Alloy, H. Asonen, M. Lindroos, M. Pessa, P. Prasad, R. Rao, A. Bansil
Arun Bansil
We present angle-resolved photoemission spectra from the low-index faces of CuAl single crystals using 16.85- and 21.22-eV radiation, together with the computed bulk electronic structure of the alloy within the framework of the muffin-tin coherent-potential approximation (CPA). The d-band complex of Cu is found to suffer shifts of less than 0.1 eV on alloying, whereas the states of s-p symmetry are lowered in energy by as much as on the order of 1 eV. The dispersion curve of the uppermost valence band is measured and with the extrapolation of this curve to the Fermi energy (EF), the Fermi-surface radii along …
Coherent-Potential And Average T-Matrix Approximations For Disordered Muffin-Tin Alloys: 1. Formalism, A. Bansil
Arun Bansil
The average density of states 〈ρ(E)〉 and the component charge density associated with an A(B) atom in the alloy, 〈ρA(B)(E)〉, are discussed for the disordered alloy AₓB₁₋ₓ within the framework of the muffintin Hamiltonian. A new version of the average t-matrix (ATA) is developed. The structure in the spectral density function, 〈ρ(k,E)〉, in the coherent-potential approximation (or the new ATA) is seen to result from not only the Bloch-type states in the medium of coherent-potential effective atoms tCP (or the average t-atoms 〈t〉) but also from non-Bloch-type impurity levels arising when a single A or B atom …
Multiple-Scattering Theory Of Itinerant Electron Magnetism In Random Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Multiple-Scattering Theory Of Itinerant Electron Magnetism In Random Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Arun Bansil
We discuss the equilibrium electronic structure of a random binary alloy within the framework of a spin-dependent muffin-tin Hamiltonian. The disorder is treated on the basis of the single-site approximations (SSA), especially the average t-matrix and the coherent potential approximations. The local-spin-density (LSD) functional approach is employed to relate the electron and the spin densities with the atomic potentials, thus providing a fully self-consistent description of the ground-state properties of the random alloy. By using the atomic magnetic moments as expansion parameters, a Stoner-type linearized form of the full SSA-LSD formalism is developed. This analysis yields insights into the nature …
Induced Superconductivity In Noncuprate Layers Of The Bi₂Sr₂Cacu₂O₈+Δ High-Temperature Superconductor: Modeling Of Scanning Tunneling Spectra, Ilpo Suominen, Jouko Nieminen, R. Markiewicz, A. Bansil
Induced Superconductivity In Noncuprate Layers Of The Bi₂Sr₂Cacu₂O₈+Δ High-Temperature Superconductor: Modeling Of Scanning Tunneling Spectra, Ilpo Suominen, Jouko Nieminen, R. Markiewicz, A. Bansil
Arun Bansil
We analyze how the coherence peaks observed in scanning tunneling spectroscopy (STS) of cuprate high-temperature superconductors are transferred from the cuprate layer to the oxide layers adjacent to the STS microscope tip. For this purpose, we have carried out a realistic multiband calculation for the superconducting state of Bi₂Sr₂CaCu₂O₈₊δ (Bi2212) assuming a short-range d-wave pairing interaction confined to the nearest-neighbor Cu dₓ2₋y2 orbitals. The resulting anomalous matrix elements of the Green’s function allow us to monitor how pairing is then induced not only within the cuprate bilayer but also within and across other layers and …
Application Of Coherent-Potential Approximation To Disordered Muffin-Tin Alloys, A. Bansil
Application Of Coherent-Potential Approximation To Disordered Muffin-Tin Alloys, A. Bansil
Arun Bansil
I report implementation of the coherent-potential approximation for obtaining the electronic density of states and component charge densities in disordered muffin-tin alloys. Illustrative results for CuₓNi₁₋ₓ are presented. The extent to which the self-consistency in treating disorder influences the electronic spectrum is considered.
Reconstructing The Bulk Fermi Surface And Superconducting Gap Properties From Neutron Scattering Experiments, Tanmoy Das, R. Markiewicz, A. Bansil
Reconstructing The Bulk Fermi Surface And Superconducting Gap Properties From Neutron Scattering Experiments, Tanmoy Das, R. Markiewicz, A. Bansil
Arun Bansil
We develop an analytical tool to extract bulk electronic properties of unconventional superconductors from inelastic neutron scattering spectra. We show that the upward and downward branches of the spin excitation spectra have distinct origins, with the upper branch representing a gapped spin-wave dispersion and the lower branch associated with Bogoliubov quasiparticle scattering on the Fermi surface. Combined, they produce an "hourglass" dispersion with 45 degrees rotation of the spectrum, as found experimentally. The downward dispersion can be inverted to reveal the Fermi momentum dispersion of the single-particle spectrum as well as the corresponding superconducting (SC) gap function, analogously to the …
Topological Electronic Structure In Half-Heusler Topological Insulators, W. Al-Sawai, Hsin Lin, R. Markiewicz, L. Wray, Y. Xia, S. Xu, M. Hasan, A. Bansil
Topological Electronic Structure In Half-Heusler Topological Insulators, W. Al-Sawai, Hsin Lin, R. Markiewicz, L. Wray, Y. Xia, S. Xu, M. Hasan, A. Bansil
Arun Bansil
We have investigated band structures of a series of 28 ternary half-Heusler compounds MM'X of MgAgAs type, where M=(Lu, La, Sc, Y) and M'X=(PtBi, AuPb, PdBi, PtSb, AuSn, NiBi, PdSb). Our results show that the Z₂ topological order is due to a single band inversion at the Γ point. In native states, these half-Heusler compounds are identified as being topologically nontrivial semimetals, or nontrivial metals, or trivial insulators, which can be turned into insulating thin films on suitable substrates. Our analysis reveals a straightforward relationship which connects the band inversion strength (extent of deviation from the critical point) to the …
Energy Dependence Of Experimental Be Compton Profiles, S. Huotari, K. Hamalainen, S. Manninen, S. Kaprzyk, A. Bansil, W. Caliebe, T. Buslaps, V. Honkimaki, P. Suortti
Energy Dependence Of Experimental Be Compton Profiles, S. Huotari, K. Hamalainen, S. Manninen, S. Kaprzyk, A. Bansil, W. Caliebe, T. Buslaps, V. Honkimaki, P. Suortti
Arun Bansil
High-resolution Compton scattering measurements on Be single crystals along three main crystallographic directions ([10.0], [11.0], and [00.1]) have been carried out using incident photon energies of 10, 29, and 56 keV to study the energy dependence of the scattering cross:section. The experimental Compton profiles are in good agreement with theoretical profiles employing the local density approximation-based band theory framework. Extensive comparisons between the computed and measured profiles, their first derivatives, and anisotropies defined as differences between various pairs of profiles show an excellent level of accord. The details related to the Fermi surface are clearly seen in the experimental Compton …
One-Band Tight-Binding Model Parametrization Of The High-Tc Cuprates Including The Effect Of Kz Dispersion, R. Markiewicz, S. Sahrakorpi, M. Lindroos, Hsin Lin, A. Bansil
One-Band Tight-Binding Model Parametrization Of The High-Tc Cuprates Including The Effect Of Kz Dispersion, R. Markiewicz, S. Sahrakorpi, M. Lindroos, Hsin Lin, A. Bansil
Arun Bansil
We discuss the effects of interlayer hopping and the resulting kz dispersion in the cuprates within the framework of the one-band tight-binding model Hamiltonian. Specific forms of the dispersion relations in terms of the in-plane hopping parameters t, t′, t″, and t‴ and the effective interlayer hopping tz in La₂₋ₓSrₓCuO₄ (LSCO) and Nd₂₋ₓCeₓCuO₄ (NCCO) and the added intracell hopping tbi between the CuO₂ bilayers in Bi₂Sr₂CaCu₂O₈ (Bi2212) are presented. The values of the “bare” parameters are obtained via fits with the first-principles local-density-approximation- (LDA-) based band structures in LSCO, NCCO, and Bi2212. The corresponding “dressed” parameter sets which account for …
Fermi Surface Evolution And Collapse Of The Mott Pseudogap In Nd2-Xcexcuo4±Δ, C. Kusko, R. Markiewicz, M. Lindroos, A. Bansil
Fermi Surface Evolution And Collapse Of The Mott Pseudogap In Nd2-Xcexcuo4±Δ, C. Kusko, R. Markiewicz, M. Lindroos, A. Bansil
Arun Bansil
Fermi surface (FS) maps and spectral intensities obtained recently in Nd₂₋ₓCeₓCuO₄±δ via high resolution ARPES measurements are analyzed using mean-field Hartree Fock and self-consistent renormalization computations within the framework of the one-band t-t′-t″-U Hubbard model Hamiltonian. We show that the remarkable observed crossover of the FS from small to large sheets reflects a reduction in the value of the effective Hubbard U with increasing electron doping and the collapse of the correlation induced Mott pseudogap just above optimal doping.
Compton Profiles For Polycrystalline Cuxni1-X Alloys: Theory And Experiment, R. Benedek, R. Prasad, S. Manninen, B. Sharma, A. Bansil, P. Mijnarends
Compton Profiles For Polycrystalline Cuxni1-X Alloys: Theory And Experiment, R. Benedek, R. Prasad, S. Manninen, B. Sharma, A. Bansil, P. Mijnarends
Arun Bansil
We present experimental and theoretical Compton profiles, J(q), for a series of CuₓNi₁₋ₓ alloys. This is the first comprehensive study of Compton profiles in an alloy system. The experiments were carried out using 60-keV γ rays on five polycrystalline alloy samples with Cu concentrations x=0.40,0.50,0.55,0.60,0.65 and on pure Cu and pure Ni. Our computations of J(q) are based on the Korringa-Kohn-Rostoker coherent-potential approximation scheme for treating the average electronic spectrum of the alloy. The theory reproduces the main features of the observed Compton profiles. The experimental Compton profiles show a nearly linear dependence on concentration while the theoretically predicted Compton …
Electronic Structure And Magnetism Of Fe$_{3-X}$V$_{X}$X (X=Si, Ga, And Al) Alloys By The Kkr-Cpa Method, A. Bansil, S. Kaprzyk, P. Mijnarends, J. Tobola
Electronic Structure And Magnetism Of Fe$_{3-X}$V$_{X}$X (X=Si, Ga, And Al) Alloys By The Kkr-Cpa Method, A. Bansil, S. Kaprzyk, P. Mijnarends, J. Tobola
Arun Bansil
We present first principles charge- and spin-selfconsistent electronic structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X for three different metalloids X=(Si, Ga and Al). In these calculations we use the methodology based on the Korringa-Kohn- Rostoker formalism and the coherent-potential approximation (KKR-CPA), generalized to treat disorder in multi-component complex alloys.
Competing Order Scenario Of Two-Gap Behavior In Hole-Doped Cuprates, Tanmoy Das, R. Markiewicz, A. Bansil
Competing Order Scenario Of Two-Gap Behavior In Hole-Doped Cuprates, Tanmoy Das, R. Markiewicz, A. Bansil
Arun Bansil
Angle-dependent studies of the gap function provide evidence for the coexistence of two distinct gaps in hole doped cuprates, where the gap near the nodal direction scales with the superconducting transition temperature Tc, while that in the antinodal direction scales with the pseudogap temperature. We present model calculations which show that most of the characteristic features observed in the recent angle-resolved photoemission spectroscopy (ARPES) as well as scanning tunneling microscopy (STM) two-gap studies are consistent with a scenario in which the pseudogap has a non-superconducting origin in a competing phase. Our analysis indicates that, near optimal doping, superconductivity can quench …
Dyson Orbitals, Quasi-Particle Effects And Compton Scattering, B. Barbiellini, A. Bansil
Dyson Orbitals, Quasi-Particle Effects And Compton Scattering, B. Barbiellini, A. Bansil
Arun Bansil
Dyson orbitals play an important role in understanding quasi-particle effects in the correlated ground state of a many-particle system and are relevant for describing the Compton scattering cross section beyond the frameworks of the impulse approximation (IA) and the independent particle model (IPM). Here we discuss corrections to the Kohn-Sham energies due to quasi-particle effects in terms of Dyson orbitals and obtain a relatively simple local form of the exchange-correlation energy. Illustrative examples are presented to show the usefulness of our scheme.
Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. Markiewicz, A. Bansil
Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. Markiewicz, A. Bansil
Arun Bansil
We discuss doping dependencies of the electronic structure and Fermi surface of the monolayer Tl$_{2-x}$Cu$_x$Ba$_2$CuO$_{6+\delta}$ (Tl2201). The TlO bands are found to be particularly sensitive to doping in that these bands rapidly move to higher energies as holes are added into the system. Such doping effects beyond the rigid band picture should be taken into account in analyzing and modeling the electronic spectra of the cuprates.