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## Full-Text Articles in Physics

Two-Dimensional Folding Technique For Enhancing Fermi Surface Signatures In The Momentum Density: Application To Compton Scattering Data From An Al-3 At. % Li Disordered Alloy, I. Matsumoto, J. Kwiatkowska, F. Maniawski, M. Itou, H. Kawata, N. Shiotani, S. Kaprzyk, P. E. Mijnarends, B. Barbiellini, A. Bansil

#### Two-Dimensional Folding Technique For Enhancing Fermi Surface Signatures In The Momentum Density: Application To Compton Scattering Data From An Al-3 At. % Li Disordered Alloy, I. Matsumoto, J. Kwiatkowska, F. Maniawski, M. Itou, H. Kawata, N. Shiotani, S. Kaprzyk, P. E. Mijnarends, B. Barbiellini, A. Bansil

*Bernardo Barbiellini*

We present a technique for enhancing Fermi surface (FS) signatures in the two-dimensional (2D) distribution obtained after the 3D momentum density in a crystal is projected along a specific direction in momentum space. These results are usEFul for investigating fermiology via high-resolution Compton scattering and positron annihilation spectroscopies. We focus on the particular case of the (110) projection in a fcc crystal where the standard approach based on the use of the Lock-Crisp-West (LCW) folding theorem fails to give a clear FS image due to the strong overlap with FS images obtained through projection from higher Brillouin zones. We show ...

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

*Bernardo Barbiellini*

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 ...

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

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

*Bernardo Barbiellini*

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.

Fermi-Surface Study Of Ba₁₋ₓKₓBio₃, S. Sahrakorpi, B. Barbiellini, R. Markiewicz, S. Kaprzyk, M. Lindroos, A. Bansil

#### Fermi-Surface Study Of Ba₁₋ₓKₓBio₃, S. Sahrakorpi, B. Barbiellini, R. Markiewicz, S. Kaprzyk, M. Lindroos, A. Bansil

*Bernardo Barbiellini*

We present all-electron computations of the three-dimensional (3D) Fermi surfaces (FS’s) in Ba₁₋ₓKₓBiO₃ for a number of different compositions based on the self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation approach for incorporating the effects of Ba/K substitution. By assuming a simple cubic structure throughout the composition range, the evolution of the nesting and other features of the FS of the underlying pristine phase is correlated with the onset of various structural transitions with K doping. A parametrized scheme for obtaining an accurate 3D map of the FS in Ba₁₋ₓKₓBiO₃ for an arbitrary doping level is developed. We remark on the ...

Dyson Orbitals, Quasi-Particle Effects And Compton Scattering, B. Barbiellini, A. Bansil

#### Dyson Orbitals, Quasi-Particle Effects And Compton Scattering, B. Barbiellini, A. Bansil

*Bernardo Barbiellini*

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.

Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil

#### Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil

*Bernardo Barbiellini*

We treat the non-relativistic Compton scattering process in which an incoming photon scatters from an N-electron many-body state to yield an outgoing photon and a recoil electron, without invoking the commonly used frameworks of either the impulse approximation (IA) or the independent particle model (IPM). An expression for the associated triple differential scattering cross section is obtained in terms of Dyson orbitals, which give the overlap amplitudes between the N-electron initial state and the (N-1) electron singly ionized quantum states of the target. We show how in the high energy transfer regime, one can recover from our general formalism the ...

Fermi-Surface Study Of Ba₁₋ₓKₓBio₃, S. Sahrakorpi, B. Barbiellini, R. Markiewicz, S. Kaprzyk, M. Lindroos, A. Bansil

*Robert Markiewicz*

We present all-electron computations of the three-dimensional (3D) Fermi surfaces (FS’s) in Ba₁₋ₓKₓBiO₃ for a number of different compositions based on the self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation approach for incorporating the effects of Ba/K substitution. By assuming a simple cubic structure throughout the composition range, the evolution of the nesting and other features of the FS of the underlying pristine phase is correlated with the onset of various structural transitions with K doping. A parametrized scheme for obtaining an accurate 3D map of the FS in Ba₁₋ₓKₓBiO₃ for an arbitrary doping level is developed. We remark on the ...

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

*Hsin Lin*

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 ...

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 ...

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.

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

#### 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.

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 ...

*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 ...

Fermi-Surface Study Of Ba₁₋ₓKₓBio₃, S. Sahrakorpi, B. Barbiellini, R. S. Markiewicz, S. Kaprzyk, M. Lindroos, A. Bansil

#### Fermi-Surface Study Of Ba₁₋ₓKₓBio₃, S. Sahrakorpi, B. Barbiellini, R. S. Markiewicz, S. Kaprzyk, M. Lindroos, A. Bansil

*Arun Bansil*

We present all-electron computations of the three-dimensional (3D) Fermi surfaces (FS’s) in Ba₁₋ₓKₓBiO₃ for a number of different compositions based on the self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation approach for incorporating the effects of Ba/K substitution. By assuming a simple cubic structure throughout the composition range, the evolution of the nesting and other features of the FS of the underlying pristine phase is correlated with the onset of various structural transitions with K doping. A parametrized scheme for obtaining an accurate 3D map of the FS in Ba₁₋ₓKₓBiO₃ for an arbitrary doping level is developed. We remark on the ...

Two-Dimensional Folding Technique For Enhancing Fermi Surface Signatures In The Momentum Density: Application To Compton Scattering Data From An Al-3 At. % Li Disordered Alloy, I. Matsumoto, J. Kwiatkowska, F. Maniawski, M. Itou, H. Kawata, N. Shiotani, S. Kaprzyk, P. E. Mijnarends, B. Barbiellini, A. Bansil

*Arun Bansil*

We present a technique for enhancing Fermi surface (FS) signatures in the two-dimensional (2D) distribution obtained after the 3D momentum density in a crystal is projected along a specific direction in momentum space. These results are usEFul for investigating fermiology via high-resolution Compton scattering and positron annihilation spectroscopies. We focus on the particular case of the (110) projection in a fcc crystal where the standard approach based on the use of the Lock-Crisp-West (LCW) folding theorem fails to give a clear FS image due to the strong overlap with FS images obtained through projection from higher Brillouin zones. We show ...

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.

Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil

#### Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil

*Arun Bansil*

We treat the non-relativistic Compton scattering process in which an incoming photon scatters from an N-electron many-body state to yield an outgoing photon and a recoil electron, without invoking the commonly used frameworks of either the impulse approximation (IA) or the independent particle model (IPM). An expression for the associated triple differential scattering cross section is obtained in terms of Dyson orbitals, which give the overlap amplitudes between the N-electron initial state and the (N-1) electron singly ionized quantum states of the target. We show how in the high energy transfer regime, one can recover from our general formalism the ...