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- ARPES (13)
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- Bi₂Sr₂CaCu₂O₈+δ (6)
- Fermi energy (6)
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- Bi₂Sr₂CaCu₂O₈ (3)
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- Matrix element effects (3)
- Model Hamiltonian (3)
- Muffin-tin Hamiltonian (3)
- Nd₂₋ₓCeₓCuO₄ (3)
- Optical theorem (3)
- STM (3)
- Angle-resolved photoemission spectroscopy (2)
- Angle-resovled photoemission spectroscopy (2)
- AₓB₁₋ₓ (2)
- Bi2212 (2)
- Coherent potential (2)
- CuAl (2)
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Articles 1 - 30 of 98
Full-Text Articles in Physics
Bulk Fermi Surface And Momentum Density In Heavily Doped La₂₋ₓsrₓcuo₄ Using High-Resolution Compton Scattering And Positron Annihilation Spectroscopies, W. Al-Sawai, B. Barbiellini, Y. Sakurai, M. Itou, P. E. Mijnarends, R. S. Markiewicz, S. Kaprzyk, S. Wakimoto, M. Fujita, S. Basak, H. Lin, Yung Jui Wang, S. W. H. Eijt, H. Schut, K. Yamada, A. Bansil
Bulk Fermi Surface And Momentum Density In Heavily Doped La₂₋ₓsrₓcuo₄ Using High-Resolution Compton Scattering And Positron Annihilation Spectroscopies, W. Al-Sawai, B. Barbiellini, Y. Sakurai, M. Itou, P. E. Mijnarends, R. S. Markiewicz, S. Kaprzyk, S. Wakimoto, M. Fujita, S. Basak, H. Lin, Yung Jui Wang, S. W. H. Eijt, H. Schut, K. Yamada, A. Bansil
Arun Bansil
We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La₂₋ₓSrₓCuO₄ by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra …
Fermi-Surface Topology And Low-Lying Electronic Structure Of The Iron-Based Superconductor Ca₁₀(Pt₃As₈)(Fe₂As₂)₅, Madhab Neupane, Chang Liu, Su-Yang Xu, Yung-Jui Wang, Ni Ni, J. M. Allred, N. Alidoust, Hsin Lin, R. S. Markiewicz, A. Bansil, R. J. Cava, M. Z. Hasan
Fermi-Surface Topology And Low-Lying Electronic Structure Of The Iron-Based Superconductor Ca₁₀(Pt₃As₈)(Fe₂As₂)₅, Madhab Neupane, Chang Liu, Su-Yang Xu, Yung-Jui Wang, Ni Ni, J. M. Allred, N. Alidoust, Hsin Lin, R. S. Markiewicz, A. Bansil, R. J. Cava, M. Z. Hasan
Arun Bansil
We report a study of low-energy electronic structure and Fermi surface topology for the recently discovered iron-based superconductor Ca₁₀(Pt₃As₈)(Fe₂As₂)₅(the 10-3-8 phase, with Tc∼8 K), via angle-resolved photoemission spectroscopy (ARPES). Despite its triclinic crystal structure, ARPES results reveal a fourfold symmetric band structure with the absence of Dirac-cone-like Fermi dots (related to magnetism) found around the Brillouin zone corners in other iron-based superconductors. Considering that the triclinic lattice and structural supercell arise from the Pt₃As₈ intermediary layers, these results indicate that those layers couple only weakly to the FeAs layers in this new superconductor at least near the surface, which has …
Electron Momentum-Space Densities And Fermi Surface Of Li100-Xmgx (0 <~ X <~ 40) Alloys: Compton Scattering Experiment Versus Theory, G. Stutz, F. Wohlert, A. Kaprolat, W. Schulke, Y. Sakurai, Y. Tanaka, M. Ito, H. Kawata, N. Shiotani, S. Kaprzyk, A. Bansil
Electron Momentum-Space Densities And Fermi Surface Of Li100-Xmgx (0 <~ X <~ 40) Alloys: Compton Scattering Experiment Versus Theory, G. Stutz, F. Wohlert, A. Kaprolat, W. Schulke, Y. Sakurai, Y. Tanaka, M. Ito, H. Kawata, N. Shiotani, S. Kaprzyk, A. Bansil
Arun Bansil
Directional Compton profiles (CP's) of Li₁₀₀₋ₓMgₓ(0≤x≤40) were measured for (11)12 directions of the momentum transfer q with (0.14) 0.16 a.u. (a.u. = atomic units: h = e = m = 1) momentum space resolution using synchrotron x rays, monochromatized to (31) 59 keV (values in brackets refer to x = 0). The total experimental valence electron CP's, their second derivatives, and the associated directional differences were compared with the corresponding Korringa-Kohn-Rostoker-coherent-potential-approximation-local-density-approximation (KKR-CPA-LDA) computations. Discrepancies between measurements and calculations are partly traced back to an inadequate treatment of electron correlation effects within the LDA framework. The three-dimensional (3D) valence-electron momentum density, …
Site-Selectivity Properties Of The Angle-Resolved Photoemission Matrix Element In Bi₂Sr₂Cacu₂O₈, S. Sahrakorpi, M. Lindroos, A. Bansil
Site-Selectivity Properties Of The Angle-Resolved Photoemission Matrix Element In Bi₂Sr₂Cacu₂O₈, S. Sahrakorpi, M. Lindroos, A. Bansil
Arun Bansil
We show that the angle-resolved photoemission (ARPES) spectra for emission from the bonding as well as the antibonding Fermi-surface sheet in Bi₂Sr₂CaCu₂O₈ possess remarkable site, selectivity properties, in that the emission for photon energies less than 25 eV is dominated by pd excitations from just the O sites in the CuO₂ planes. There is little contribution from Cu electrons to the ARPES intensity, even though the initial states at the Fermi energy contain an admixture of Cu-d and O-p electrons. We analyze the origin of this effect by considering the nature of the associated dipole matrix element in detail and …
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 …
First-Principles Treatment Of Disorder Effects In Complex Alloys: A Study Of Baxk1-Xbio3 And Bapb1-Xbixo3, A. Bansil, S. Kaprzyk
First-Principles Treatment Of Disorder Effects In Complex Alloys: A Study Of Baxk1-Xbio3 And Bapb1-Xbixo3, A. Bansil, S. Kaprzyk
Arun Bansil
We have developed a self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation (KKR-CPA) approach to treat multiatom-per-unit-cell systems in order to study disorder effects in complex materials on a first-principles basis. Electronic structure of the high-Tc superconducting perovskites BaₓK₁₋ₓBiO₃ and BaPb₁₋ₓBiₓO₃ is discussed. KKR-CPA results for x=0.1,0.2,...,0.9, as well as for the limiting single-impurity cases x=0.0 and x=1.0 are used to delineate rigid-band and non-rigid-band effects in the spectrum. McMillan-Hopfield parameters over the entire composition range are presented.
Matrix Element Effects In Angle-Resolved Photoemission From Bi₂Sr₂Cacu₂O₈: Energy And Polarization Dependencies, Final State Spectrum, Spectral Signatures Of Specific Transitions, And Related Issues, M. Lindroos, S. Sahrakorpi, A. Bansil
Matrix Element Effects In Angle-Resolved Photoemission From Bi₂Sr₂Cacu₂O₈: Energy And Polarization Dependencies, Final State Spectrum, Spectral Signatures Of Specific Transitions, And Related Issues, M. Lindroos, S. Sahrakorpi, A. Bansil
Arun Bansil
We have carried out extensive simulations of the angle-resolved photoemission (ARPES) intensity in Bi2212 within the one-step- and three-step-type models using a first-principles band theory framework. The focus is on understanding the behavior of emissions from the antibonding and bonding bands arising from the CuO₂ bilayers around the M̅ (π,0) symmetry point. The specific issues addressed include: Dependencies of the photointensity on the energy and polarization of the incident light; character of the initial and final states involved as well as the spectrum of the relevant final states; and changes in the spectral intensity as a function of the perpendicular …
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 …
Fermi Surface, Ground-State Electronic Structure, And Positron Experiments In Yba₂Cu₃O₇, A. Bansil, R. Pankaluoto, R. S. Rao, P. E. Mijnarends, W. Dlugosz, R. Prasad, L. C. Smedskjaer
Fermi Surface, Ground-State Electronic Structure, And Positron Experiments In Yba₂Cu₃O₇, A. Bansil, R. Pankaluoto, R. S. Rao, P. E. Mijnarends, W. Dlugosz, R. Prasad, L. C. Smedskjaer
Arun Bansil
We present calculations of electron-positron momentum density in YBa₂Cu₃O₇ based on band theory in the local-density approximation. Theoretical predictions are in semiquantitative accord with the corresponding two-dimensional positron-annihilation angular-correlation measurements. These results indicate that the conventional local-density-approximation band-theory picture provides a reasonable description of the ground-state electronic structure and the Fermi surface of YBa₂Cu₃O₇. Several Fermi-surface-related features are suggested in the positron spectra for the first time.
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 …
Angle-Resolved Photoemission Spectra, Electronic Structure, And Spin-Dependent Scattering In Ni1-Xfex Permalloys, P. E. Mijnarends, S. Sahrakorpi, M. Lindroos, A. Bansil
Angle-Resolved Photoemission Spectra, Electronic Structure, And Spin-Dependent Scattering In Ni1-Xfex Permalloys, P. E. Mijnarends, S. Sahrakorpi, M. Lindroos, A. Bansil
Arun Bansil
We present the all-electron charge and spin self-consistent electronic structure of Ni₁₋ₓFeₓ Permalloys for a range of Fe concentrations. using the first-principles Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) scheme to treat disorder and the local spin density approximation to incorporate exchange-correlation effects. Recent high-resolution angle-resolved photoemission spectroscopy (ARPES) experiments on Ni0.90Fe0.10 and Ni0.80Fe0.20 Permalloys are analyzed in terms of the spectral density function, ABkⅡ, k⊥ = 0, EF), computed from the KKR-CPA Green function for kⅡ values varying along the Γ-K direction in the Brillouin zone. The widths of the majority as well as the minority spin peaks in the theoretical …
Fermi Surface Of A Disordered Cu-Al-Alloy Single Crystal Studied By High-Resolution Compton Scattering And Electron Diffraction, J. Kwiatkowska, F. Maniawski, I. Matsumoto, H. Kawata, N. Shiotani, L. Lityriska, S. Kaprzyk, A. Bansil
Fermi Surface Of A Disordered Cu-Al-Alloy Single Crystal Studied By High-Resolution Compton Scattering And Electron Diffraction, J. Kwiatkowska, F. Maniawski, I. Matsumoto, H. Kawata, N. Shiotani, L. Lityriska, S. Kaprzyk, A. Bansil
Arun Bansil
We have measured high resolution Compton scattering profiles for momentum transfer along a series of 28 independent directions from Cu0.842Al0.158 disordered alloy single crystals with normals to the surfaces oriented along the [100], [110], and [111] directions. The experimental spectra are interpreted via parallel first-principles KKR-CPA (Korringa-Kohn-Rostoker coherent-potential approximation) computations of these directional profiles. The Fermi surface determined by inverting the Compton data is found to be in good agreement with the KKR-CPA predictions. An electron diffraction study of the present Cu0.842Al0.158 sample is additionally undertaken to gain insight into short-range ordering effects. The scattering pattern displays not only the …
Fermi-Surface Properties Of Alpha-Phase Alloys Of Copper With Zinc, R. Prasad, S. C. Papadopoulos, A. Bansil
Fermi-Surface Properties Of Alpha-Phase Alloys Of Copper With Zinc, R. Prasad, S. C. Papadopoulos, A. Bansil
Arun Bansil
We consider the Fermi-surface properties of the α-Cu1-cZnc system over the composition range 0≤c≤0.3. Our calculations are based on the application of the self-consistent coherent potential approximation to the muffin-tin Hamiltonian. The predictions of the theory with respect to the radii kneck, k100, and k110, and the size and shape of the alloy Fermi surface in several planes in the Brillouin zone are in good agreement with the available positron annihilation measurements and with the predictions of the rigid-band model. We discuss how the hitherto unmeasured disorder smearing of the alloy Fermi surface may be amenable to a direct experimental …
Raising Bi-O Bands Above The Fermi Energy Level Of Hole-Doped Bi₂Sr₂Cacu₂O₈+Δ And Other Cuprate Superconductors, Hsin Lin, S. Sahrakorpi, R. S. Markiewicz, A. Bansil
Raising Bi-O Bands Above The Fermi Energy Level Of Hole-Doped Bi₂Sr₂Cacu₂O₈+Δ And Other Cuprate Superconductors, Hsin Lin, S. Sahrakorpi, R. S. Markiewicz, A. Bansil
Arun Bansil
The Fermi surface (FS) of Bi₂Sr₂CaCu₂O₈₊δ (Bi2212) predicted by band theory displays Bi-related pockets around the (π,0) point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy (EF) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole doping the Bi-O bands drop below EF and the system self-dopes below a critical hole concentration. Computations on other Bi- as well as Tl- and Hg-based compounds indicate …
Composition Dependence Of Optical Gaps In Copper-Based Hume-Rothery Alloys, R. S. Rao, R. Prasad, A. Bansil
Composition Dependence Of Optical Gaps In Copper-Based Hume-Rothery Alloys, R. S. Rao, R. Prasad, A. Bansil
Arun Bansil
We discuss the composition dependence of a number of critical energy gaps in the Cu-based Hume-Rothery alloys CuZn, CuAl, and CuGe. Our computations, employing the Korringa-Kohn-Rostoker coherent-potential approach, provide a remarkably simple and consistent explanation of a variety of available optical experiments on these systems. Polyvalent impurities are found to influence the spectrum of Cu in a manner which varies strongly from one solute to another.
Gutzwiller Magnetic Phase Diagram Of The Cuprates, R. S. Markiewicz, J. Lorenzana, G. Seibold, A. Bansil
Gutzwiller Magnetic Phase Diagram Of The Cuprates, R. S. Markiewicz, J. Lorenzana, G. Seibold, A. Bansil
Arun Bansil
A general constructive procedure is presented for analyzing magnetic instabilities in two-dimensional materials, in terms of (predominantly) double nesting, and applied to Hartree-Fock plus random-phase approximation (HF+RPA) and Gutzwiller approximation plus RPA calculations of the Hubbard model. Applied to the cuprates, it is found that competing magnetic interactions are present only for hole doping, between half filling and the Van Hove singularity. While HF+RPA instabilities are present at all dopings (for sufficiently large Hubbard U), in a Gutzwiller approximation they are restricted to a doping range close to the range of relevance for the physical cuprates. The same model would …
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 …
Paramagnon-Induced Dispersion Anomalies In The Cuprates, R. S. Markiewicz, S. Sahrakorpi, A. Bansil
Paramagnon-Induced Dispersion Anomalies In The Cuprates, R. S. Markiewicz, S. Sahrakorpi, A. Bansil
Arun Bansil
We report the self-energy associated with random-phase approximation magnetic susceptibility in the hole-doped Bi₂Sr₂CuO₆ (Bi2201) and the electron-doped Nd₂₋ₓCeₓCuO₄ (NCCO) in the overdoped regime within the framework of a one-band Hubbard model. A strong weight is found in the magnetic spectrum around (π,0) at about 360 meV in Bi2201 and 640 meV in NCCO, which yields dispersion anomalies in accord with the recently observed “waterfall” effects in the cuprates.
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 …
Effect Of Orbital Symmetry Of The Tip On Scanning Tunneling Spectra Of Bi₂Sr₂Cacu₂O₈+Δ, Ilpo Suominen, Jouko Nieminen, R. S. Markiewicz, A. Bansil
Effect Of Orbital Symmetry Of The Tip On Scanning Tunneling Spectra Of Bi₂Sr₂Cacu₂O₈+Δ, Ilpo Suominen, Jouko Nieminen, R. S. Markiewicz, A. Bansil
Arun Bansil
We discuss how variations in the scanning tunneling microscope (STM) tip, whether unintentional or intentional, can lead to changes in topographic images and dI/dV spectra. We consider the possibility of utilizing functionalized tips in order to improve the sensitivity of STM experiments to local irregularities at the surface or hidden below the surface layers. The change in the tip symmetry can radically alter the contrast of the topographic image due to changes in tip-surface overlap. The dI/dV curves change their shape according to which sample bands the tip orbital tends to overlap. In addition, relative phases between competing tunneling channels …
Electronic-Structure Of Copper-Rich Copper-Gold Alloys, H. Asonen, C. J. Barnes, M. Pessa, R. S. Rao, A. Bansil
Electronic-Structure Of Copper-Rich Copper-Gold Alloys, H. Asonen, C. J. Barnes, M. Pessa, R. S. Rao, A. Bansil
Arun Bansil
We present and discuss angle-resolved photoemission measurements from the (111) and (100) faces of CuAu single crystals containing 10 at. % Au in the bulk, together with computations of complex-energy bands and densities of states in the Cu₉₀Au₁₀ random alloy. Our calculations permit a good understanding of the shifts and smearings in the spectrum of Cu arising from the addition of Au with respect to the Cu d-band complex, the (111) Shockley state, and the (100) Tamm state. The observed position and width of the Au-induced structure in the density of states is also in good accord with the theoretical …
Coexisting Pseudogap, Charge-Transfer-Gap, And Mott-Gap Energy Scales In The Resonant Inelastic X-Ray Scattering Spectra Of Electron-Doped Cuprate Superconductors, Susmita Basak, Tanmoy Das, Hsin Lin, M. Z. Hasan, R. S. Markiewicz, A. Bansil
Coexisting Pseudogap, Charge-Transfer-Gap, And Mott-Gap Energy Scales In The Resonant Inelastic X-Ray Scattering Spectra Of Electron-Doped Cuprate Superconductors, Susmita Basak, Tanmoy Das, Hsin Lin, M. Z. Hasan, R. S. Markiewicz, A. Bansil
Arun Bansil
We present a computation of Cu K-edge resonant inelastic x-ray scattering (RIXS) spectra for electron-doped cuprates, which includes coupling to bosonic fluctuations. Comparison with experiment over a wide range of energy and momentum transfers allows us to identify the signatures of three key normal-state energy scales: the pseudogap, charge-transfer gap, and Mott gap. The calculations involve a three-band Hubbard Hamiltonian based on dₓ2₋y2 and O pₓ, py orbitals, with a self-energy correction which arises due to spin and charge fluctuations. Our theory reproduces characteristic features, e.g., gap collapse, large spectral weight broadening, and spectral weight transfer as a function of …
Coherent-Potential And Average T-Matrix Approximations For Disordered Muffin-Tin Alloys: 2. Application To Realistic Systems, A. Bansil
Arun Bansil
In an earlier article, the electronic spectrum of the disordered alloy AₓB₁₋ₓ, using the coherent-potential (CPA) and the average t-matrix (ATA) approximations, was discussed within the framework of the muffintin Hamiltonian. Using the illustrative examples of CuₓNi₁₋ₓ and CuₓZn₁₋ₓ, the present paper exposes the physically relevant aspects of the electronic spectra of disordered transition and noble-metal alloys. Bloch spectral densities, complex energy bands, impurity levels, and average total and component densities of states are considered. We also discuss how the effects of transfer of charge between the constituents on their atomic potentials can be included in a semiempirical manner in …
Positron-Annihilation Study Of The Electronic Structure Of Cu91ge9, P. E. Mijnarends, L. P.L.M. Rabou, K. E.H.M. Hanssen, A. Bansil
Positron-Annihilation Study Of The Electronic Structure Of Cu91ge9, P. E. Mijnarends, L. P.L.M. Rabou, K. E.H.M. Hanssen, A. Bansil
Arun Bansil
A novel effect of alloying on the electron momentum density in a disordered α-Cu₉₁Ge₉ alloy is reported. The effect, which is the appearance of a bump in the derivative spectra at low momenta, is predicted by theory employing the coherent-potential approximation and is observed in two-dimensional angular correlation experiments on the alloy. It reflects the presence of an s-p impurity band far below the Fermi level. Accurate experimental values for the Fermi-surface radii k100 and k110 and for the associated disorder-induced smearings in CuGe are also reported for the first time.
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.
Failure Of T-J Models In Describing Doping Evolution Of Spectral Weight In X-Ray Scattering, Optical, And Photoemission Spectra Of Cuprates, R. S. Markiewicz, Tanmoy Das, A. Bansil
Failure Of T-J Models In Describing Doping Evolution Of Spectral Weight In X-Ray Scattering, Optical, And Photoemission Spectra Of Cuprates, R. S. Markiewicz, Tanmoy Das, A. Bansil
Arun Bansil
We have analyzed experimental evidence for an anomalous transfer of spectral weight from high-to low-energy scales in both electron-and hole-doped cuprates as a function of doping. X-ray scattering, optical, and photoemission spectra are all found to show that the high-energy spectral weight decreases with increasing doping at a rate much faster than predictions of the large U-limit calculations. The observed doping evolution is however well described by an intermediate coupling scenario where the effective Hubbard U is comparable to the bandwidth. The experimental spectra across various spectroscopies are inconsistent with fixed-U exact diagonalization or quantum Monte Carlo calculations, and suggest …
Effects Of The Positron Spatial-Distribution On Momentum Densities In Random Muffin-Tin Alloys, A. Bansil, P. E. Mijnarends
Effects Of The Positron Spatial-Distribution On Momentum Densities In Random Muffin-Tin Alloys, A. Bansil, P. E. Mijnarends
Arun Bansil
We consider the problem of incorporating positron spatial distribution effects on the two-photon momentum density 〈ρ2γ(p)〉 in a disordered alloy. 〈ρ2γ(p)〉 formally involves the average 〈GG₊〉 of the product of electron and positron Green's functions. Our approach utilizes the framework of the average-t-matrix and coherent-potential approximations to treat disorder in the alloy and neglects the vertex corrections which arise in evaluating 〈GG₊〉. The influence of disorder on the positron state is delineated in terms of the properties of 〈G₊〉. Illustrative results for Cu, Cu₇₅Ni₂₅, Cu₅₀Ni₅₀, and Ni are presented and discussed.
A-Axis Projected Electron-Positron-Momentum Density And Positron-Annihilation Spectra In Yba₂Cu₃O₇-X, P. Pankaluoto, A. Bansil, L. C. Smedskjaer, P. E. Mijnarends
A-Axis Projected Electron-Positron-Momentum Density And Positron-Annihilation Spectra In Yba₂Cu₃O₇-X, P. Pankaluoto, A. Bansil, L. C. Smedskjaer, P. E. Mijnarends
Arun Bansil
We present and discuss theoretical and experimental a-axis-projected two-dimensional angular correlation of annihilation radiation (2D-ACAR) spectra from YBa₂Cu₃O₇₋ₓ. The experiment involved an untwinned metallic single crystal of YBa₂Cu₃O6.9 at room temperature. The calculations have been carried out within the conventional first-principles band-theory framework based on the local-density approximation; the positron state is treated in the independent-particle model. After the as-observed 2DACAR spectrum is corrected for an isotropic background, a good accord is found between not only the overall shape but also the fine structure in the measured and computed spectra, some discrepancies not-withstanding. Extensive analysis shows that the experimental spectrum …
Positron Two-Dimensional Angular-Correlation-Of-Annihilation-Radiation Study Of Untwinned Yba2cu3o6.9 In The A-Axis Projection, L. C. Smedskjaer, A. Bansil, U. Welp, Y. Fang, K. G. Bailey
Positron Two-Dimensional Angular-Correlation-Of-Annihilation-Radiation Study Of Untwinned Yba2cu3o6.9 In The A-Axis Projection, L. C. Smedskjaer, A. Bansil, U. Welp, Y. Fang, K. G. Bailey
Arun Bansil
We present a two-dimensional (2D)-ACAR positron annihilation study of an untwinned YBa₂Cu₃O6.9 metallic sample in the a-axis projection; all existing data from untwinned samples have employed the c projection. The data show a clear presence of the Cu-O chain related ridge Fermi surface extending along the ΓZ direction and two associated umklapp images at higher momenta. These results are consistent with the previously investigated c projection of the momentum density in YBa₂Cu₃O6.9 and do not appear to indicate a strong localization of these electron states along the c direction. We compare and contrast the structures in 2D-ACAR’s in the a …