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- ARPES (11)
- Angle-resolved photoemission (9)
- Compton scattering (8)
- Cuprates (7)
- Bi₂Sr₂CaCu₂O₈+δ (5)
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- Fermi energy (5)
- Electron momentum density (4)
- Electronic structure (4)
- Muffin-tin alloys (4)
- Bi₂Sr₂CaCu₂O₈ (3)
- Cu (3)
- Fermi level (3)
- Fermi surface (3)
- Korringa-Kohn-Rostoker coherent-potential-approximation (3)
- La₂₋ₓSrₓCuO₄ (3)
- Matrix element effects (3)
- Model Hamiltonian (3)
- Muffin-tin Hamiltonian (3)
- Nd₂₋ₓCeₓCuO₄ (3)
- Optical theorem (3)
- Strongly correlated electrons (3)
- Angle-resolved photoemission spectroscopy (2)
- Angle-resovled photoemission spectroscopy (2)
- Bi2212 (2)
- Compton profiles (2)
- CuPd alloys (2)
- Directional Compton profiles (2)
- Doping dependence (2)
- Doping evolution (2)
- FS (2)
Articles 31 - 60 of 81
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Electron Momentum Densities In Disordered Muffin-Tin Alloys, A. Bansil, R. S. Rao, P. E. Mijnarends, L. Schwartz
Electron Momentum Densities In Disordered Muffin-Tin Alloys, A. Bansil, R. S. Rao, P. E. Mijnarends, L. Schwartz
Arun Bansil
The application of average t-matrix (ATA) and coherent potential (CPA) approximations to the calculation of average electron momentum density ρ(p) in random muffin-tin alloys AₓB₁₋ₓ is considered. The necessary equations for the general matrix elements of the operators describing scattering by the CPA atom and also by an A or B atom embedded in the effective medium are derived. Various versions of the ATA for ρ(p) are discussed. Several ρ(p) curves calculated on the basis of the CPA and ATA in CuₓNi₁₋ₓ are presented. These results are used to delineate the effects on ρ(p) of self-consistency in the treatment of …
Nodeless D-Wave Superconducting Pairing Due To Residual Antiferromagnetism In Underdoped Pr2-Xcexcuo4-Δ, Tanmoy Das, R. S. Markiewicz, A. Bansil
Nodeless D-Wave Superconducting Pairing Due To Residual Antiferromagnetism In Underdoped Pr2-Xcexcuo4-Δ, Tanmoy Das, R. S. Markiewicz, A. Bansil
Arun Bansil
We investigate the doping dependence of the penetration depth versus temperature in electron-doped Pr₂₋ₓCeₓCuO4-δ using a model which assumes the uniform coexistence of (mean-field) antiferromagnetism and superconductivity. Despite the presence of a dₓ2₋y2 pairing gap in the underlying spectrum, we find nodeless behavior of the low-T penetration depth in the underdoped case, in accord with experimental results. As doping increases, a linear-in-T behavior of the penetration depth, characteristic of d-wave pairing, emerges as the lower magnetic band crosses the Fermi level and creates a nodal Fermi surface pocket.
Optical Theorem And Multiple-Scattering Theory: Electronic States In Disordered Transion-Metals, L. Schwartz, A. Bansil
Optical Theorem And Multiple-Scattering Theory: Electronic States In Disordered Transion-Metals, L. Schwartz, A. Bansil
Arun Bansil
In disordered systems, apparently reasonable decoupling procedures can lead to negative densities of electronic states near resonant d bands. By applying the optical theorem to the multiple-scattering series we can determine a prior whether a given decoupling will necessarily yield positive results. Since none of the extensions of the coherent-potential approximation to amorphous systems is found to meet this requirement, we propose a new scheme which is both self-consistent and guaranteed to give a positive spectrum.
Nonmonotonic Dₓ2₋Y2 Superconducting Gap In Electron-Doped Pr0.89lace0.11cuo4: Evidence Of Coexisting Antiferromagnetism And Superconductivity?, Tanmoy Das, R. S. Markiewicz, A. Bansil
Nonmonotonic Dₓ2₋Y2 Superconducting Gap In Electron-Doped Pr0.89lace0.11cuo4: Evidence Of Coexisting Antiferromagnetism And Superconductivity?, Tanmoy Das, R. S. Markiewicz, A. Bansil
Arun Bansil
Recent experiments on Pr0.89LaCe0.11CuO₄ observe an anisotropic spin-correlation gap and a nonmonotonic superconducting (SC) gap, which we analyze within the framework of a t-t′-t″-t‴-tiv-U model with a dₓ2−y2 pairing interaction including a third-harmonic contribution. By introducing a realistic broadening of the quasiparticle spectrum to reflect small-angle scattering, our computations explain the experimental observations, especially the presence of a maximum in the leading-edge gap in the vicinity of the hot spots. Our analysis suggests that the material behaves like a two-band superconductor with the d-wave third harmonic acting as the interband pairing gap, and that the antiferromagnetic and SC orders coexist …
Fermi Surface And Electron-Positron Momentum Density In Yba₂Cu₃O₇, A. Bansil, P. E. Mijnarends, L. C. Smedskjaer
Fermi Surface And Electron-Positron Momentum Density In Yba₂Cu₃O₇, A. Bansil, P. E. Mijnarends, L. C. Smedskjaer
Arun Bansil
By folding the local-density-approximation (LDA) band-theory-based electron-positron momentum density into the first Brillouin zone, we find that signatures from all the Fermi-surface sheets can be obtained in YBa₂Cu₃O₇, including in particular the Cu-O plane sheets. Our theoretical predictions appear to be in reasonable overall accord with the corresponding measurements by positron-annihilation two-dimensional angular correlation of annihilation radiation (2D-ACAR) of Smedskjaer et al., which have been interpreted in terms of Fermi surfaces. The Cu-O chain-related (electron) states appear to be substantially modified from LDA predictions. However, no firm conclusions concerning the existence of the Fermi surface in YBa₂Cu₃O₇ can at the …
Proposal To Determine The Fermi-Surface Topology Of A Doped Iron-Based Superconductor Using Bulk-Sensitive Fourier-Transform Compton Scattering, Yung Jui Wang, Hsin Lin, B. Barbiellini, P. E. Mijnarends, S. Kaprzyk, R. S. Markiewicz, A. Bansil
Proposal To Determine The Fermi-Surface Topology Of A Doped Iron-Based Superconductor Using Bulk-Sensitive Fourier-Transform Compton Scattering, Yung Jui Wang, Hsin Lin, B. Barbiellini, P. E. Mijnarends, S. Kaprzyk, R. S. Markiewicz, A. Bansil
Arun Bansil
We have carried out first-principles calculations of the Compton scattering spectra to demonstrate that the filling of the hole Fermi surface in LaO₁₋ₓFₓFeAs produces a distinct signature in the Fourier-transformed Compton spectrum when the momentum transfer vector lies along the [100] direction. We thus show how the critical concentration xc
Electron Momentum Density In Disordered Muffin-Tin Cu1-Xnix In The Average-T-Matrix Approximation, P. E. Mijnarends, A. Bansil
Electron Momentum Density In Disordered Muffin-Tin Cu1-Xnix In The Average-T-Matrix Approximation, P. E. Mijnarends, A. Bansil
Arun Bansil
In an earlier article we discussed the formalism for evaluating the average electron-momentum density in a random binary alloy by using the average-t-matrix approximation to treat the disorder and muffin-tin potentials to represent the constituent atoms. The present paper considers the application of this formalism to Cu₁₋ₓNiₓ over a range of alloy compositions. The characteristic effects of disorder on the spectral momentum density 〈ρ(p,E)〉 are delineated. In discussing the momentum density 〈ρ(p)〉 we focus on how this quantity changes as x increases from 0 to 1 and the Ni d band develops from a virtual bound state below the Fermi …
Surface States And Angle-Resolved Photoemission Spectra From Nd₂₋ₓceₓcuo₄, M. Lindroos, A. Bansil
Surface States And Angle-Resolved Photoemission Spectra From Nd₂₋ₓceₓcuo₄, M. Lindroos, A. Bansil
Arun Bansil
By carrying out first-principles angle-resolved photoemission (ARPES) computations within the local-density-approximation-based band theory framework, we predict the existence of surface states on the (001) surface of the superconductor Nd₂₋ₓCeₓCuO₄ (NCCO). Two surface state bands are identified in the vicinity of the Fermi energy. The associated states possess quite different characteristics in terms of their binding energy, dispersion with k∥, and the polarization and photon energy dependence. Our theoretical predictions offer new insight into the existing ARPES data on NCCO with which they are consistent.
Observation Of A Tamm-Type State On Cu0.9al0.1(100) Surface: Disorder Effects And Bulk Electronic Structure Of An Alloy, M. Pessa, H. Asonen, R. S. Rao, R. Prasad, A. Bansil
Observation Of A Tamm-Type State On Cu0.9al0.1(100) Surface: Disorder Effects And Bulk Electronic Structure Of An Alloy, M. Pessa, H. Asonen, R. S. Rao, R. Prasad, A. Bansil
Arun Bansil
The electronic structure of a CU0.9Al0.1(100) single crystal has been studied with use of an angle-resolved photoemission technique. An intrinsic Tamm-type surface state is found to exist in the disordered alloy. The linewidth of the surface state is analyzed to deduce the disorder-induced smearing of energy levels. These and other experimental results are discussed in terms of the computed band structure of the alloy on the basis of coherent-potential approximation applied to a realistic muffin-tin Hamiltonian.
High Resolution Compton Scattering Study Of Be, K. Hamalainen, S. Manninen, C. C. Kao, W. Caliebe, J. B. Hastings, A. Bansil, S. Kaprzyk, P. M. Platzman
High Resolution Compton Scattering Study Of Be, K. Hamalainen, S. Manninen, C. C. Kao, W. Caliebe, J. B. Hastings, A. Bansil, S. Kaprzyk, P. M. Platzman
Arun Bansil
We have carried out high-resolution Compton scattering measurements from two single crystals of Be ([00.1] and [11.0]), together with highly accurate all-electron first-principles computations of the profiles within the band theory framework. The Compton data were collected using a newly constructed crystal spectrometer at a record momentum resolution varying between 0.023 and 0.032 a.u. (full width at half maximum) with 8 keV x rays from a synchrotron source. Although the overall shapes of the measured and computed spectra are in good accord, the fine structure in the data shows significant discrepancies with respect to the local density approximation based theoretical …
High-Resolution Angle-Resolved Photoemission Spectra From Ni(100): Matrix Element Effects And Spin-Resolved Initial And Final State Bands, S. Sahrakorpi, M. Lindroos, A. Bansil
High-Resolution Angle-Resolved Photoemission Spectra From Ni(100): Matrix Element Effects And Spin-Resolved Initial And Final State Bands, S. Sahrakorpi, M. Lindroos, A. Bansil
Arun Bansil
We have carried out extensive one- and three-step angle-resolved photoemission spectroscopy (ARPES) intensity computations on Ni(100) within the band theory framework based on the local spin-density approximation. The results show a good overall level of accord with the recent high-resolution ARPES experiments on Ni(100) which probe the majority- and minority-spin Σ₁ band along the Γ-K direction near the Fermi energy (EF), uncertainties inherent in our first-principles approach notwithstanding. The k‖ and energy dependencies of various spectral features are delineated in terms of the interplay between changes in the initial- and final-state bands and the associated transition matrix elements. The remarkable …
Electronic Structure Of Au70pd30 Disordered Alloy, E. Arola, C. J. Barnes, R. S. Rao, A. Bansil
Electronic Structure Of Au70pd30 Disordered Alloy, E. Arola, C. J. Barnes, R. S. Rao, A. Bansil
Arun Bansil
We present angle-resolved photoemission (normal-emission) measurements from the (100) surface of a disordered Au₇₀Pd₃₀ alloy single crystal using He i, Ne i, He ii, and Ne ii excitations. The experimental results are interpreted via fully relativistic Korringa-Kohn-Rostoker coherent-potential-approximation computations of complex-energy bands, spectral densities, and total and site-decomposed densities of states in the alloy. Our measurements and calculations indicate that the main effects of adding Pd to Au are the following: (i) the appearance of a Pd-derived d-band complex with small dispersion, distinctly above the Au d-band edge, centered about 1 eV below the Fermi energy, (ii) the Au-derived d-band …
Emergence Of Multiple Fermi Surface Maps In Angle-Resolved Photoemission From Bi₂Sr₂Cacu₂O₈+Δ, M. C. Asensio, J. Avila, L. Roca, A. Tejeda, G. D. Gu, M. Lindroos, R. S. Markiewicz, A. Bansil
Emergence Of Multiple Fermi Surface Maps In Angle-Resolved Photoemission From Bi₂Sr₂Cacu₂O₈+Δ, M. C. Asensio, J. Avila, L. Roca, A. Tejeda, G. D. Gu, M. Lindroos, R. S. Markiewicz, A. Bansil
Arun Bansil
We report angle-resolved photoemission spectra (ARPES) for emission from the Fermi energy (EF) over a large area of the (kx,ky) plane using 21.2 and 32 eV photon energies in two distinct polarizations from an optimally doped single crystal of Bi₂Sr₂CaCu₂O₈₊δ (Bi2212), together with extensive first-principles simulations of the ARPES intensities. The results display a wide-ranging level of accord between theory and experiment, demonstrating that the ARPES matrix elements can produce a striking variety of Fermi surface maps, especially in the presence of secondary features arising from modulations of the underlying tetragonal system. Our analysis demonstrates how the energy and polarization …
Role Of Oxygen Electrons In The Metal-Insulator Transition In The Magnetoresistive Oxide La2-2xsr1+2xmn2o7 Probed By Compton Scattering, B. Barbiellini, A. Koizumi, P. E. Mijnarends, W. Al-Sawai, Hsin Lin, T. Nagao, K. Hirota, M. Itou, Y. Sakurai, A. Bansil
Role Of Oxygen Electrons In The Metal-Insulator Transition In The Magnetoresistive Oxide La2-2xsr1+2xmn2o7 Probed By Compton Scattering, B. Barbiellini, A. Koizumi, P. E. Mijnarends, W. Al-Sawai, Hsin Lin, T. Nagao, K. Hirota, M. Itou, Y. Sakurai, A. Bansil
Arun Bansil
We have studied the [100]-[110] anisotropy of the Compton profile in the bilayer manganite. Quantitative agreement is found between theory and experiment with respect to the anisotropy in the two metallic phases (i.e., the low temperature ferromagnetic and the colossal magnetoresistant phase under a magnetic field of 7 T). Robust signatures of the metal-insulator transition are identified in the momentum density for the paramagnetic phase above the Curie temperature. We interpret our results as providing direct evidence for the transition from the metalliclike to the admixed ionic-covalent bonding accompanying the magnetic transition. The number of electrons involved in this phase …
Systematic Doping Evolution Of The Underlying Fermi Surface Of La₂₋ₓsrₓcuo₄, T. Yoshida, X. J. Zhou, K. Tanaka, W. L. Yang, Z. Hussain, Z. X. Shen, A. Fujimori, S. Sahrakorpi, M. Lindroos, R. S. Markiewicz, A. Bansil, Seiki Komiya, Yoichi Ando, H. Eisaki, T. Kakeshita, S. Uchida
Systematic Doping Evolution Of The Underlying Fermi Surface Of La₂₋ₓsrₓcuo₄, T. Yoshida, X. J. Zhou, K. Tanaka, W. L. Yang, Z. Hussain, Z. X. Shen, A. Fujimori, S. Sahrakorpi, M. Lindroos, R. S. Markiewicz, A. Bansil, Seiki Komiya, Yoichi Ando, H. Eisaki, T. Kakeshita, S. Uchida
Arun Bansil
We have performed a systematic doping-dependent study of La₂₋ₓSrₓCuO₄ (LSCO) (0.03 <= x <= 0.3) by angle-resolved photoemWe have performed a systematic doping-dependent study of La₂₋ₓSrxCuO₄ (LSCO) (0.03⩽x⩽0.3) by angle-resolved photoemission spectroscopy. Over this entire doping range, the underlying “Fermi surface” determined from the low-energy spectral weight approximately satisfies Luttinger’s theorem, even down to the lightly doped region. This is in strong contrast to the results on Ca₂₋ₓNaₓCuO₂Cl₂ (Na-CCOC), which show a clear deviation from Luttinger’s theorem. We correlate these differences between LSCO and Na-CCOC with differences in the behavior of chemical potential shift and spectral weight transfer induced by …
Optical Theorem And Multiple-Scattering Theory: Electronic States In Substitutional Alloys, L. Schwartz, A. Bansil
Optical Theorem And Multiple-Scattering Theory: Electronic States In Substitutional Alloys, L. Schwartz, A. Bansil
Arun Bansil
When multiple-scattering theory is used to describe the electronic properties of disordered transition-metal systems, decoupling procedures which appear to be physically reasonable can lead to negative densities of states in the vicinity of the resonant d bands. We present a method, based on the application of the optical theorem to the total scattering operator, that allows us to determine a priori which approximation schemes can be relied upon to produce a positive spectrum. The application of this method to substitutionally disordered binary alloys is discussed here. We find that both the average-t-matrix and coherent-potential approximations will always yield nonnegative densities …
Renormalization Of F Levels Away From The Fermi Energy In Electron Excitation Spectroscopies: Density-Functional Results For Nd2-Xcexcuo4, T. Jarlborg, B. Barbiellini, H. Lin, R. S. Markiewicz, A. Bansil
Renormalization Of F Levels Away From The Fermi Energy In Electron Excitation Spectroscopies: Density-Functional Results For Nd2-Xcexcuo4, T. Jarlborg, B. Barbiellini, H. Lin, R. S. Markiewicz, A. Bansil
Arun Bansil
Relaxation energies for photoemission where an occupied electronic state is excited and for inverse photoemission where an empty state is filled are calculated within the density-functional theory with application to Nd₂₋ₓCeₓCuO₄. The associated relaxation energies are obtained by computing differences in total energies between the ground state and an excited state in which one hole or one electron is added into the system. The relaxation energies of f electrons are found to be of the order of several eV’s, indicating that f bands will appear substantially away from the Fermi energy (EF) in their spectroscopic images, even if these bands …
Effective-Medium Theory Of Electronic States In Structurally Disordered Metals: Application To Liquid Cu, L. Huisman, D. Nicholson, L. Schwartz, A. Bansil
Effective-Medium Theory Of Electronic States In Structurally Disordered Metals: Application To Liquid Cu, L. Huisman, D. Nicholson, L. Schwartz, A. Bansil
Arun Bansil
We consider the application of the effective-medium approximation (EMA) to the muffin-tin model of a liquid metal. The spherical symmetry of the average liquid is used to reduce the momentum (k)-dependent self-consistency requirements of the theory to a form in which they involve one-dimensional rather than three-dimensional integrations. We also show that, within the EMA, a closed expression for the integrated density of states can be derived, and that this expression provides a useful check on the convergence of the self-consistent equations. The theory is applied to liquid Cu. The self-consistent equations converge without difficulty and the resulting electronic spectrum …
Magnetic Mechanism Of Quasiparticle Pairing In Hole-Doped Cuprate Superconductors, R. S. Markiewicz, A. Bansil
Magnetic Mechanism Of Quasiparticle Pairing In Hole-Doped Cuprate Superconductors, R. S. Markiewicz, A. Bansil
Arun Bansil
We have computed α2F’s for the hole-doped cuprates within the framework of the one-band Hubbard model, where the full magnetic response of the system is treated properly. The d-wave pairing weight α2Fd is found not only to contain a low-energy peak due to excitations near (π,π) expected from neutron-scattering data but also to display substantial spectral weight at higher energies due to contributions from other parts of the Brillouin zone as well as pair-breaking ferromagnetic excitations at low energies. The resulting solutions of the Eliashberg equations yield transition temperatures and gaps comparable to the experimentally observed values, suggesting that magnetic …
Electronic Structure Of The Metallic Ground State Of La2−2xsr1+2xmn2o7 For X≈0.59 And Comparison With X=0.36,0.38 Compounds As Revealed By Angle-Resolved Photoemission, Z. Sun, J. F. Douglas, Q. Wang, D. S. Dessau, A. V. Fedorov, H. Lin, S. Sahrakorpi, B. Barbiellini, R. S. Markiewicz, A. Bansil, H. Zheng, J. F. Mitchell
Electronic Structure Of The Metallic Ground State Of La2−2xsr1+2xmn2o7 For X≈0.59 And Comparison With X=0.36,0.38 Compounds As Revealed By Angle-Resolved Photoemission, Z. Sun, J. F. Douglas, Q. Wang, D. S. Dessau, A. V. Fedorov, H. Lin, S. Sahrakorpi, B. Barbiellini, R. S. Markiewicz, A. Bansil, H. Zheng, J. F. Mitchell
Arun Bansil
Using angle-resolved photoemission spectroscopy, we present the electronic structure of the metallic ground state of La₂₋₂ₓSr₁₊₂ₓMn₂O₇ (x≈0.59) and interpret the results in terms of first-principles band-structure computations, of which the generalized gradient approximation yields the best agreement with the experimental data. No bilayer-split bands are found in this compound, indicating the near degeneracy of electronic states in the neighboring MnO₂ layers due to its A-type antiferromagnetic structure. The d₃z2₋r2 states near the zone center were not observed, which is also consistent with its A-type antiferromagnetic structure. Near the Fermi level, a kink in the dispersion reveals an important electron-phonon many-body …
Spectral Decomposition And Matrix Element Effects In Scanning Tunneling Spectroscopy Of Bi₂Sr₂Cacu₂O₈₊Δ, Jouko Nieminen, Ilpo Suominen, R. S. Markiewicz, Hsin Lin, A. Bansil
Spectral Decomposition And Matrix Element Effects In Scanning Tunneling Spectroscopy Of Bi₂Sr₂Cacu₂O₈₊Δ, Jouko Nieminen, Ilpo Suominen, R. S. Markiewicz, Hsin Lin, A. Bansil
Arun Bansil
We present a Green’s function-based framework for modeling the scanning tunneling spectrum from the normal as well as the superconducting state of complex materials where the nature of the tunneling process—i.e., the effect of the tunneling “matrix element,” is properly taken into account. The formalism is applied to the case of optimally doped Bi₂Sr₂CaCu2=₂O8+δ (Bi2212) high-Tc superconductor using a large tight-binding basis set of electron and hole orbitals. The results show clearly that the spectrum is modified strongly by the effects of the tunneling matrix element and that it is not a simple replica of the local density of states …
Special Photon Energies For Extracting The Bosonic Spectral Function Mediating Superconductivity In Bi₂Sr₂Cacu₂O₈ Via Angle-Resolved Photoemission Spectroscopy, M. Lindroos, R. S. Markiewicz, A. Bansil
Special Photon Energies For Extracting The Bosonic Spectral Function Mediating Superconductivity In Bi₂Sr₂Cacu₂O₈ Via Angle-Resolved Photoemission Spectroscopy, M. Lindroos, R. S. Markiewicz, A. Bansil
Arun Bansil
We delineate the complex nature of the angle-resolved photoemission spectroscopy (ARPES) matrix element in Bi₂Sr₂CaCu₂O₈ and identify photon energies where the matrix element is insensitive to wave vector and/or frequency. These special photon energies provide a unique route for extracting the spectral function of the bosonic glue mediating superconductivity and for obtaining self-energies more generally via ARPES experiments.
Green’S Function And A Generalized Lloyd Formula For The Density Of States In Disordered Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Green’S Function And A Generalized Lloyd Formula For The Density Of States In Disordered Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Arun Bansil
We consider the Korringa-Kohn-Rostoker coherent-potential-approximation Green’s function for a disordered system of muffin-tin potentials and evaluate its integral over the Wigner-Seitz cell rigorously throughout the complex energy plane. The resulting expression is shown to possess a perfect derivative form, provided the angular-momentum summations are extended to infinity; for a finite angular-momentum cutoff this result is valid to a good approximation. For real energies our expression constitutes a generalization of the Lloyd formula for the density of states. The conventional Lloyd formula contains unphysical singularities that are not only unsatisfactory from a formal viewpoint, but also make its use increasingly cumbersome …
Optical Model-Solution To The Competition Between A Pseudogap Phase And A Charge-Transfer-Gap Phase In High-Temperature Cuprate Superconductors, Tanmoy Das, R. S. Markiewicz, A. Bansil
Optical Model-Solution To The Competition Between A Pseudogap Phase And A Charge-Transfer-Gap Phase In High-Temperature Cuprate Superconductors, Tanmoy Das, R. S. Markiewicz, A. Bansil
Arun Bansil
We present a theoretical framework for a quantitative understanding of the full doping dependence of the optical spectra of the cuprates. In accord with experimental observations, the computed spectra show how the high-energy charge-transfer (CT) gap features persist in the overdoped regime even after the midinfrared (MIR) peak originating from the pseudogap has collapsed in a quantum critical point. In this way, we reconcile the opposing tendencies of the MIR and CT peaks to shift in opposite directions in the optical spectra with increasing doping. The competition between the pseudogap and the CT gap also results in rapid loss of …
Spin Texture On The Warped Dirac-Cone Surface States In Topological Insulators, Susmita Basak, Hsin Lin, L. A. Wray, S. Y. Xu, L. Fu, M. Z. Hasan, A. Bansil
Spin Texture On The Warped Dirac-Cone Surface States In Topological Insulators, Susmita Basak, Hsin Lin, L. A. Wray, S. Y. Xu, L. Fu, M. Z. Hasan, A. Bansil
Arun Bansil
We have investigated the nature of surface states in the Bi₂Te₃ family of three-dimensional topological insulators using first-principles calculations as well as a model Hamiltonian approach. When the surface Dirac cone is warped due to Dresselhaus spin-orbit coupling in rhombohedral structures, the spin acquires a finite out-of-the-plane component. We provide a simple, minimal model to describe the in-plane spin texture of the warped surface Dirac cone observed in experiments where spins are seen to be not aligned perpendicular to the electron momentum. Our k·p model calculation reveals that this in-plane spin texture requires fifth-order Dresselhaus spin-orbit coupling terms
Nonlinear Composition Dependence Of The Fermi-Surface Dimensions In Alpha-Phase Copper-Germanium Alloys, R. Prasad, A. Bansil
Nonlinear Composition Dependence Of The Fermi-Surface Dimensions In Alpha-Phase Copper-Germanium Alloys, R. Prasad, A. Bansil
Arun Bansil
In considering the α-CU₁₀₀₋ₓGeₓ alloys on the basis of a realistic muffin-tin Hamiltonian, the most notable feature of the electronic spectra is found to be the appearance of an impurity band below the host conduction band. In accord with relevant experiments, a Fermi surface is predicted to grow at approximately half the rigid-band rate for x5 at.% Ge. This effect is related to a transition in the nature of states associated with the impurity band; these states are localized atomic s-like states for x≤0.5 and become delocalized in concentrated alloys.
Single-Dirac-Cone Topological Surface States In The Tlbise₂ Class Of Topological Semiconductors, Hsin Lin, R. S. Markiewicz, L. A. Wray, L. Fu, M. Z. Hasan, A. Bansil
Single-Dirac-Cone Topological Surface States In The Tlbise₂ Class Of Topological Semiconductors, Hsin Lin, R. S. Markiewicz, L. A. Wray, L. Fu, M. Z. Hasan, A. Bansil
Arun Bansil
We investigate several strong spin-orbit coupling ternary chalcogenides related to the (Pb,Sn)Te series of compounds. Our first-principles calculations predict the low-temperature rhombohedral ordered phase in TlBiTe₂, TlBiSe₂, and TlSbX₂ (X=Te, Se, S) to be topologically nontrivial. We identify the specific surface termination that realizes the single Dirac cone through first-principles surface state computations. This termination minimizes effects of dangling bonds, making it favorable for photoemission experiments. In addition, our analysis predicts that thin films of these materials could harbor novel 2D quantum spin Hall states, and support odd-parity topological superconductivity.
Further Analysis Of Electronic States In The Muffin-Tin Model Of A Disordered Alloy, L. Schwartz, A. Bansil
Further Analysis Of Electronic States In The Muffin-Tin Model Of A Disordered Alloy, L. Schwartz, A. Bansil
Arun Bansil
Several new results on the evaluation of the spectral function A(k⃗,E) and average density of states ρ(E) in a realistic model of a substitutional binary alloy are presented. This work is primarily concerned with the conditions under which a given approach can be relied upon to yield a non-negative spectrum. In the average t matrix and coherent-potential approximations, a link is established between the sign of A(k⃗,E) and the Argand diagram for the energy-shell matrix elements τL of the effective atomic scattering operators: If τL lies within the unitarity circle, then A(k⃗,E)>0. The connection between this result and our …
Origin Of The Electron-Hole Asymmetry In The Scanning Tunneling Spectrum Of The High-Temperature Bi₂Sr₂Cacu₂O₈+Δ Superconductor, Jouko Nieminen, Hsin Lin, R. S. Markiewicz, A. Bansil
Origin Of The Electron-Hole Asymmetry In The Scanning Tunneling Spectrum Of The High-Temperature Bi₂Sr₂Cacu₂O₈+Δ Superconductor, Jouko Nieminen, Hsin Lin, R. S. Markiewicz, A. Bansil
Arun Bansil
We have developed a material specific theoretical framework for modeling scanning tunneling spectroscopy (STS) of high-temperature superconducting materials in the normal as well as the superconducting state. Results for Bi₂Sr₂CaCu₂O₈₊δ (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states of the dₓ2₋y2 orbital of Cu. The dominant tunneling channel to the surface Bi involves the dₓ2₋y2 orbitals of the four neighboring Cu atoms. In accord with experimental observations, the computed spectrum displays a remarkable asymmetry between the processes of electron injection and extraction, which arises from contributions of Cu dz2 and …
Compton Study Of Ni75cu25 And Ni75co25 Disordered Alloys: Theory And Experiment, A. Bansil, S. Kaprzyk, A. Andrejczuk, L. Dobrzynski, J. Kwiatkowska, F. Maniawski, E. Zukowski
Compton Study Of Ni75cu25 And Ni75co25 Disordered Alloys: Theory And Experiment, A. Bansil, S. Kaprzyk, A. Andrejczuk, L. Dobrzynski, J. Kwiatkowska, F. Maniawski, E. Zukowski
Arun Bansil
We present first-principles computations of ferromagnetic electronic structures and spin-resolved Compton profiles along the three high-symmetry directions in Ni₇₅Cu₂₅ and Ni₇₅Co₂₅ disordered alloys, together with the corresponding Compton measurements from single-crystal specimens with a 137Cs source. The theoretical results are based on the use of the charge- and spin-self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation framework to treat disorder, and the local spin-density scheme for incorporating exchange-correlation effects; the lattice constants in all cases are obtained by minimizing the total energy. The majority-spin spectrum of Ni undergoes relatively small changes upon alloying with Cu or Co, and the associated majority-spin contribution to the Compton …