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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 Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 …


First-Principles Treatment Of Disorder Effects In Complex Alloys: A Study Of Baxk1-Xbio3 And Bapb1-Xbixo3, A. Bansil, S. Kaprzyk Apr 2012

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 Apr 2012

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 …


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 Apr 2012

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.


Angle-Resolved Photoemission Spectra, Electronic Structure, And Spin-Dependent Scattering In Ni1-Xfex Permalloys, P. E. Mijnarends, S. Sahrakorpi, M. Lindroos, A. Bansil Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 …


Paramagnon-Induced Dispersion Anomalies In The Cuprates, R. S. Markiewicz, S. Sahrakorpi, A. Bansil Apr 2012

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.


Effect Of Orbital Symmetry Of The Tip On Scanning Tunneling Spectra Of Bi₂Sr₂Cacu₂O₈+Δ, Ilpo Suominen, Jouko Nieminen, R. S. Markiewicz, A. Bansil Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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.


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 Apr 2012

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 Apr 2012

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 Apr 2012

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 Apr 2012

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 …


Special Directions For Brillouin-Zone Integration: Application To Density Of-States Calculations, R. Prasad, A. Bansil Apr 2012

Special Directions For Brillouin-Zone Integration: Application To Density Of-States Calculations, R. Prasad, A. Bansil

Arun Bansil

We present several large sets of special directions for cubic lattices. The question of accuracy obtainable in density-of-states and Fermi-energy evaluations in disordered alloys by using various direction sets is discussed. In this context, results on the simple cubic tight-binding band and on the model Hamiltonian for Cu are considered.


Resonating-Valence-Bond Ground State Of Lithium Nanoclusters, D. Nissenbaum, L. Spanu, C. Attaccalite, B. Barbiellini, A. Bansil Apr 2012

Resonating-Valence-Bond Ground State Of Lithium Nanoclusters, D. Nissenbaum, L. Spanu, C. Attaccalite, B. Barbiellini, A. Bansil

Arun Bansil

We have performed diffusion quantum Monte Carlo simulations of Li clusters showing that resonating-valence-bond (RVB) pairing correlations between electrons provide a substantial contribution to the cohesive energy. The RVB effects are identified in terms of electron transfers from s-like to p-like character, constituting a possible explanation for the breakdown of the Fermi-liquid picture observed in recent high-resolution Compton scattering experiments for bulk Li.


Influence Of The Third Dimension Of Quasi-Two-Dimensional Cuprate Superconductors On Angle-Resolved Photoemission Spectra, A. Bansil, M. Lindroos, S. Sahrakorpi, R. S. Markiewicz Apr 2012

Influence Of The Third Dimension Of Quasi-Two-Dimensional Cuprate Superconductors On Angle-Resolved Photoemission Spectra, A. Bansil, M. Lindroos, S. Sahrakorpi, R. S. Markiewicz

Arun Bansil

Angle-resolved photoemission spectroscopy (ARPES) presents significant simplifications in analyzing strictly two-dimensional (2D) materials, but even the most anisotropic physical systems display some residual three-dimensionality. Here we demonstrate how this third dimension manifests itself in ARPES spectra of quasi-2D materials by considering the example of the cuprate Bi₂Sr₂CaCu₂O₈ (Bi2212). The intercell, interlayer hopping, which is responsible for kz dispersion of the bands, is found to induce an irreducible broadening to the ARPES line shapes with a characteristic dependence on the in-plane momentum k‖. Our study suggests that ARPES line shapes can provide a direct spectroscopic window for establishing the existence of …


Spontaneous Magnetization And Electron Momentum Density In Three-Dimensional Quantum Dots, R. Saniz, B. Barbiellini, A. B. Denison, A. Bansil Apr 2012

Spontaneous Magnetization And Electron Momentum Density In Three-Dimensional Quantum Dots, R. Saniz, B. Barbiellini, A. B. Denison, A. Bansil

Arun Bansil

We discuss an exactly solvable model Hamiltonian for describing the interacting electron gas in a quantum dot. Results for a spherical square-well confining potential are presented. The ground state is found to exhibit striking oscillations in spin polarization with dot radius at a fixed electron density. These oscillations are shown to induce characteristic signatures in the momentum density of the electron gas, providing a route for direct experimental observation of the dot magnetization via spectroscopies sensitive to the electron momentum density.


Electronic Structure Of Cu₇₅Au₂₅ Disordered Alloy, E. Arola, R. S. Rao, A. Salokatve, A. Bansil Apr 2012

Electronic Structure Of Cu₇₅Au₂₅ Disordered Alloy, E. Arola, R. S. Rao, A. Salokatve, A. Bansil

Arun Bansil

We present angle-resolved uv photoemission (normal emission) measurements from the (100) and (111) surfaces of Cu₇₅Au₂₅ alloy single crystals, together with fully relativistic as well as nonrelativistic Korringa-Kohn-Rostoker coherent-potential-approximation calculations of complex energy bands and densities of states. A good overall accord is found between the measurements and theoretical predictions with regard to the shifts and smearings of various bulk states in the alloy. The characteristic effects of alloying Au on the electronic structure of Cu are identified; the principal Au-induced feature is 2.5 eV wide, and appears 3 eV below the Cu-derived d band in the alloy; this feature …


High-Resolution Compton Scattering Study Of Li: Asphericity Of The Fermi Surface And Electron Correlation Effects, Y. Sakurai, Y. Tanaka, A. Bansil, S. Kaprzyk, A. T. Stewart, Y. Nagashima, T. Hyodo, S. Nanao, H. Kawata, N. Shiotani Apr 2012

High-Resolution Compton Scattering Study Of Li: Asphericity Of The Fermi Surface And Electron Correlation Effects, Y. Sakurai, Y. Tanaka, A. Bansil, S. Kaprzyk, A. T. Stewart, Y. Nagashima, T. Hyodo, S. Nanao, H. Kawata, N. Shiotani

Arun Bansil

We present high-resolution Compton scattering spectra from Li single crystals together with corresponding highly accurate local-density-approximation (LDA) based computations. The data are analyzed to obtain Fermi surface radii along the three principal symmetry directions; the maximum measured anisotropy is found to be (4.6±1.0)%. Comparisons between the measured and computed spectra clearly reveal departures from the conventional one-particle LDA picture of the ground state momentum density of the electron gas. This study establishes the potential of Compton scattering as a tool for investigating Fermiology-related issues in materials.


Evolution Of Midgap States And Residual Three Dimensionality In La₂₋ₓsrₓcuo₄, S. Sahrakorpi, M. Lindroos, R. S. Markiewicz, A. Bansil Apr 2012

Evolution Of Midgap States And Residual Three Dimensionality In La₂₋ₓsrₓcuo₄, S. Sahrakorpi, M. Lindroos, R. S. Markiewicz, A. Bansil

Arun Bansil

We carry out extensive first-principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La₂₋ₓSrₓCuO₄ over a wide range of binding energies. Intercell hopping and the associated three dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g., the presence of a lower Hubbard band coexisting with midgap states in the doped insulator), a number of salient features of the experimental ARPES spectra are captured to a surprising extent when kz dispersion is properly included in the analysis.