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Full-Text Articles in Physics

A Spin-Polarized Scheme For Obtaining Quasi-Particle Energies Within The Density Functional Theory, B. Barbiellini, A. Bansil Apr 2012

A Spin-Polarized Scheme For Obtaining Quasi-Particle Energies Within The Density Functional Theory, B. Barbiellini, A. Bansil

Bernardo Barbiellini

We discuss an efficient scheme for obtaining spin-polarized quasi-particle excitation energies within the general framework of the density functional theory (DFT). Our approach is to correct the DFT eigenvalues via the electrostatic energy of a majority or minority spin electron resulting from its interaction with the associated exchange and correlation holes by using appropriate spin-resolved pair correlation functions. A version of the method for treating systems with localized orbitals, including the case of partially filled metallic bands, is considered. Illustrative results on Cu are presented.


Direct Observation Of Localization Of The Minority-Spin-Band Electrons In Magnetite Below The Verwey Temperature, Hisao Kobayashi, Toshihiro Nagao, Masayoshi Itou, Sakae Todo, Bernardo Barbiellini, Peter E. Mijnarends, Arun Bansil, Nobuhiko Sakai Apr 2012

Direct Observation Of Localization Of The Minority-Spin-Band Electrons In Magnetite Below The Verwey Temperature, Hisao Kobayashi, Toshihiro Nagao, Masayoshi Itou, Sakae Todo, Bernardo Barbiellini, Peter E. Mijnarends, Arun Bansil, Nobuhiko Sakai

Bernardo Barbiellini

Two-dimensional spin-uncompensated momentum density distributions, $\rho_{\rm s}^{2D}({\bf p})$s, were reconstructed in magnetite at 12K and 300K from several measured directional magnetic Compton profiles. Mechanical de-twinning was used to overcome severe twinning in the single crystal sample below the Verwey transition. The reconstructed $\rho_{\rm s}^{2D}({\bf p})$ in the first Brillouin zone changes from being negative at 300 K to positive at 12 K. This result provides the first clear evidence that electrons with low momenta in the minority spin bands in magnetite are localized below the Verwey transition temperature.


Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil Apr 2012

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 ...


Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. S. Markiewicz, A. Bansil Apr 2012

Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. S. Markiewicz, A. Bansil

Hsin Lin

We discuss doping dependencies of the electronic structure and Fermi surface of the monolayer Tl$_{2-x}$Cu$_x$Ba$_2$CuO$_{6+\delta}$ (Tl2201). The TlO bands are found to be particularly sensitive to doping in that these bands rapidly move to higher energies as holes are added into the system. Such doping effects beyond the rigid band picture should be taken into account in analyzing and modeling the electronic spectra of the cuprates.


Direct Observation Of Localization Of The Minority-Spin-Band Electrons In Magnetite Below The Verwey Temperature, Hisao Kobayashi, Toshihiro Nagao, Masayoshi Itou, Sakae Todo, Bernardo Barbiellini, Peter E. Mijnarends, Arun Bansil, Nobuhiko Sakai Feb 2011

Direct Observation Of Localization Of The Minority-Spin-Band Electrons In Magnetite Below The Verwey Temperature, Hisao Kobayashi, Toshihiro Nagao, Masayoshi Itou, Sakae Todo, Bernardo Barbiellini, Peter E. Mijnarends, Arun Bansil, Nobuhiko Sakai

Arun Bansil

Two-dimensional spin-uncompensated momentum density distributions, $\rho_{\rm s}^{2D}({\bf p})$s, were reconstructed in magnetite at 12K and 300K from several measured directional magnetic Compton profiles. Mechanical de-twinning was used to overcome severe twinning in the single crystal sample below the Verwey transition. The reconstructed $\rho_{\rm s}^{2D}({\bf p})$ in the first Brillouin zone changes from being negative at 300 K to positive at 12 K. This result provides the first clear evidence that electrons with low momenta in the minority spin bands in magnetite are localized below the Verwey transition temperature.


Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. Markiewicz, A. Bansil Feb 2011

Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. Markiewicz, A. Bansil

Arun Bansil

We discuss doping dependencies of the electronic structure and Fermi surface of the monolayer Tl$_{2-x}$Cu$_x$Ba$_2$CuO$_{6+\delta}$ (Tl2201). The TlO bands are found to be particularly sensitive to doping in that these bands rapidly move to higher energies as holes are added into the system. Such doping effects beyond the rigid band picture should be taken into account in analyzing and modeling the electronic spectra of the cuprates.


A Spin-Polarized Scheme For Obtaining Quasi-Particle Energies Within The Density Functional Theory, B. Barbiellini, A. Bansil Feb 2011

A Spin-Polarized Scheme For Obtaining Quasi-Particle Energies Within The Density Functional Theory, B. Barbiellini, A. Bansil

Arun Bansil

We discuss an efficient scheme for obtaining spin-polarized quasi-particle excitation energies within the general framework of the density functional theory (DFT). Our approach is to correct the DFT eigenvalues via the electrostatic energy of a majority or minority spin electron resulting from its interaction with the associated exchange and correlation holes by using appropriate spin-resolved pair correlation functions. A version of the method for treating systems with localized orbitals, including the case of partially filled metallic bands, is considered. Illustrative results on Cu are presented.


Compton Scattering Beyond The Impulse Approximation, I. G. Kaplan, B. Barbiellini, A. Bansil Feb 2011

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 ...


Dielectric Signatures Of Lattice Instabilities At 32k And 245k In $La_{2-Y}Sr_{Y}Mo_{4+X}$ (M=Cu,Ni) Cuprates And Nickelates, P. Parimi, N. Hakim, F. Chou, S. Cheong, S. Sridhar Feb 2011

Dielectric Signatures Of Lattice Instabilities At 32k And 245k In $La_{2-Y}Sr_{Y}Mo_{4+X}$ (M=Cu,Ni) Cuprates And Nickelates, P. Parimi, N. Hakim, F. Chou, S. Cheong, S. Sridhar

Srinivas Sridhar

New dielectric transitions are observed at common temperatures 32K and 245K, in isostructural $La_{2}CuO_{4+x}$ and $La_{5/3}Sr_{1/3}NiO_{4},$ that are signatures of local lattice (octahedral) instabilities. The present dielectric transitions reveal new aspects of the phase diagram of the perovskite cuprates and nickelates. They suggest that competition and coexistence of superconductivity with dielectricity occurs that is analogous to that between superconductivity and anti-ferromagnetism. These results also indicate that inhomogeneous electronic states, such as charge stripes and oxygen ordering, are strongly connected to underlying lattice instabilities.


Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. S. Markiewicz, A. Bansil Feb 2011

Effect Of Hole Doping On The Electronic Structure Of Tl2201, S. Sahrakorpi, Hsin Lin, R. S. Markiewicz, A. Bansil

Robert Markiewicz

We discuss doping dependencies of the electronic structure and Fermi surface of the monolayer Tl$_{2-x}$Cu$_x$Ba$_2$CuO$_{6+\delta}$ (Tl2201). The TlO bands are found to be particularly sensitive to doping in that these bands rapidly move to higher energies as holes are added into the system. Such doping effects beyond the rigid band picture should be taken into account in analyzing and modeling the electronic spectra of the cuprates.


Compressibility Of A Two-Dimensional Hole Gas In A Tilted Magnetic Field, Maryam Rahimi, M. Sakr, S. Kravchenko, S. Dultz, H. Jiang Jan 2011

Compressibility Of A Two-Dimensional Hole Gas In A Tilted Magnetic Field, Maryam Rahimi, M. Sakr, S. Kravchenko, S. Dultz, H. Jiang

Sergey Kravchenko

We have measured compressibility of a two-dimensional hole gas in p-GaAs/AlGaAs heterostructure, grown on a (100) surface, in the presence of a tilted magnetic field. It turns out that the parallel component of magnetic field affects neither the spin splitting nor the density of states. We conclude that: (a) g-factor in the parallel magnetic field is nearly zero in this system; and (b) the level of the disorder potential is not sensitive to the parallel component of the magnetic field.


Conductivity Of A Spin-Polarized Two-Dimensional Electron Liquid In The Ballistic Regime, A. A. Shashkin, E. V. Deviatov, V. T. Dolgopolov, A. A. Kapustin, S. Anissimova, A. Venkatesan, S. V. Kravchenko, T. M. Klapwijk Jan 2011

Conductivity Of A Spin-Polarized Two-Dimensional Electron Liquid In The Ballistic Regime, A. A. Shashkin, E. V. Deviatov, V. T. Dolgopolov, A. A. Kapustin, S. Anissimova, A. Venkatesan, S. V. Kravchenko, T. M. Klapwijk

Sergey Kravchenko

In the ballistic regime, the metallic temperature dependence of the conductivity in a twodimensional electron system in silicon is found to change non-monotonically with the degree of spin polarization. In particular, it fades away just before the onset of complete spin polarization but reappears again in the fully spin-polarized state, being, however, suppressed relative to the zero-field case. Analysis of the degree of the suppression allows one to distinguish between the screening and the interaction-based theories.


A Metal-Insulator Transition In 2d: Established Facts And Open Questions, S. V. Kravchenko, M. P. Sarachik Jan 2011

A Metal-Insulator Transition In 2d: Established Facts And Open Questions, S. V. Kravchenko, M. P. Sarachik

Sergey Kravchenko

The discovery of a metallic state and a metal-insulator transition (MIT) in two-dimensional (2D) electron systems challenges one of the most influential paradigms of modern mesoscopic physics, namely, that "there is no true metallic behavior in two dimensions". However, this conclusion was drawn for systems of noninteracting or weakly interacting carriers, while in all 2D systems exhibiting the metal-insulator transition, the interaction energy greatly exceeds all other energy scales. We review the main experimental findings and show that, although significant progress has been achieved in our understanding of the MIT in 2D, many open questions remain.


"Forbidden" Transitions Between Quantum Hall And Insulating Phases In P-Sige Heterostructures, M. R. Sakr, Maryam Rahimi, S. V. Kravchenko, P. T. Coleridge, R. L. Williams, J. Lapointe Jan 2011

"Forbidden" Transitions Between Quantum Hall And Insulating Phases In P-Sige Heterostructures, M. R. Sakr, Maryam Rahimi, S. V. Kravchenko, P. T. Coleridge, R. L. Williams, J. Lapointe

Sergey Kravchenko

We show that in dilute metallic p-SiGe heterostructures, magnetic field can cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating states are observed between quantum Hall states with filling factors = 1 and 2 and, for the first time, between = 2 and 3 and between = 4 and 6. The latter are in contradiction with the original global phase diagram for the quantum Hall effect. We suggest that the application of a (perpendicular) magnetic field induces insulating behaviour in metallic p-SiGe heterostructures in the same way as in Si MOSFETs. This insulator is then in competition with, and interrupted by, integer quantum Hall ...


Comment On "Theory Of Metal-Insulator Transitions In Gated Semiconductors", S. V. Kravchenko, M. P. Sarachik, D. Simonian Jan 2011

Comment On "Theory Of Metal-Insulator Transitions In Gated Semiconductors", S. V. Kravchenko, M. P. Sarachik, D. Simonian

Sergey Kravchenko

No abstract provided.


Absorption Of Nuclear Gamma Radiation By Heavy Electrons On Metallic Hydride Surfaces, A. Widom, L. Larsen Jan 2011

Absorption Of Nuclear Gamma Radiation By Heavy Electrons On Metallic Hydride Surfaces, A. Widom, L. Larsen

Allan Widom

Low energy nuclear reactions in the neighborhood of metallic hydride surfaces may be induced by ultra-low momentum neutrons. Heavy electrons are absorbed by protons or deuterons producing ultra low momentum neutrons and neutrinos. The required electron mass renormalization is provided by the interaction between surface electron plasma oscillations and surface proton oscillations. The resulting neutron catalyzed low energy nuclear reactions emit copious prompt gamma radiation. The heavy electrons which induce the initially produced neutrons also strongly absorb the prompt nuclear gamma radiation, re-emitting soft photons. Nuclear hard photon radiation away from the metallic hydride surfaces is thereby strongly suppressed.