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Current-induced spin polarization and the spin Hall effect: a quasiclassical approach

Fri, 30 Nov 2007 23:00:00 GMT

Current-induced spin polarization and the spin Hall effect: a quasiclassical approach Raimondi, Roberto; Gorini, Cosimo; Dzierzawa, Michael; Schwab, Peter 2007-12 Solid State Communications 144 524-528 The quasiclassical Green function formalism is used to describe charge and spin dynamics in the presence of spin–orbit coupling. We review the results obtained for the spin Hall effect on restricted geometries. The role of boundaries is discussed in the framework of spin diffusion equations.

Quasiclassical approach and spin–orbit coupling

Tue, 04 Mar 2008 23:00:00 GMT

Quasiclassical approach and spin–orbit coupling Gorini, Cosimo; Schwab, Peter; Dzierzawa, Michael; Raimondi, Roberto 2008-03-05 Physica E: Low-dimensional Systems and Nanostructures 40 1078-1080 We discuss the quasiclassical Green function method for a two-dimensional electron gas in the presence of spin–orbit coupling, with emphasis on the meaning of the ξ-integration procedure. As an application of our approach, we demonstrate how the spin-Hall conductivity, in the presence of spin-flip scattering, can be easily obtained from the spin-density continuity equation.

Nonlinear effects and dephasing in disordered electron systems

Thu, 31 Dec 1998 23:00:00 GMT

Nonlinear effects and dephasing in disordered electron systems Raimondi, Roberto; Schwab, Peter; Castellani, Claudio 1999 Physical Review B 60 5818 - 5831 The calculation of the dephasing time in electron systems is presented. By means of the Keldysh formalism, we discuss in a unifying way both weak localization and interaction effects in disordered systems. This allows us to show how dephasing arises both in the particle-particle channel (weak localization) and in the particle-hole channel (interaction effect). First we discuss dephasing by an external field. Besides reviewing previous work on how an external oscillating field suppresses the weak localization correction, we derive a new expression for the effect of a field on the interaction correction. We find that the latter may be suppressed by a static electric field, in contrast to weak localization. We then consider dephasing due to inelastic scattering. The ambiguities involved in the definition of the dephasing time are clarified by directly comparing the diagrammatic approach with the path-integral approach. We show that different dephasing times appear in the particle-particle and particle-hole channels. Finally we comment on recent experiments.

Andreev tunneling in quantum dots: A slave-boson approach

Thu, 31 Dec 1998 23:00:00 GMT

Andreev tunneling in quantum dots: A slave-boson approach Schwab, Peter; Raimondi, Roberto 1999 Physical Review B 59 1637 - 1640 We study a strongly interacting quantum dot connected to a normal and to a superconducting lead. By means of the slave-boson technique we investigate the low-temperature regime and discuss electrical transport through the dot. At the level of mean-field approximation we are able to discuss both limits of small and large Δ/TK, where Δ is the superconducting gap and TK is the Kondo temperature. We also find that the zero-bias anomaly in the current-voltage characteristics, which is associated with the occurrence of the Kondo resonance in the quantum dot, is enhanced in the presence of superconductivity, due to resonant Andreev scattering.

Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas

Wed, 26 Jul 2006 22:00:00 GMT

Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas Raimondi, Roberto; Gorini, Cosimo; Schwab, Peter; Dzierzawa, Michael 2006-07-27 Physical Review B-Condensed Matter and Material Physics 74 035340 We study the spin-charge coupled transport in a two-dimensional electron system using the method of quasiclassical (-integrated) Green's functions. In particular we derive the Eilenberger equation in the presence of a generic spin-orbit field. The method allows us to study spin and charge transport from ballistic to diffusive regimes and continuity equations for spin and charge are automatically incorporated. In the clean limit we establish the connection between the spin Hall conductivity and the Berry phase in momentum space. For finite systems we solve the Eilenberger equation numerically for the special case of the Rashba spin-orbit coupling and a two-terminal geometry. In particular, we calculate explicitly the spin Hall induced spin polarization in the corners, predicted by Mishchenko et al. [Phys. Rev. Lett. 93, 226602 (2004)]. Furthermore we find universal spin currents in the short-time dynamics after switching on the voltage across the sample, and calculate the corresponding spin Hall polarization at the edges. Where available, we find perfect agreement with analytical results.

Tuning the spin Hall effect in a two-dimensional electron gas

Fri, 31 Jul 2009 22:00:00 GMT

Tuning the spin Hall effect in a two-dimensional electron gas Raimondi, Roberto; Schwab, Peter 2009-08 Europhysics Letters 87 37008 We provide a theoretical framework for the electric field control of the electron spin in systems with diffusive electron motion. The approach is valid in the experimentally important case where both intrinsic and extrinsic spin-orbit interaction in a two-dimensional electron gas are present simultaneously. Surprisingly, even when the extrinsic mechanism is the dominant driving force for spin Hall currents, the amplitude of the spin Hall conductivity may be considerably tuned by varying the intrinsic spin-orbit coupling via a gate voltage. Furthermore we provide an explanation for the mechanism giving rise to the experimentally observed out-of-plane spin polarization in a (110) GaAs quantum well.

Electronic thermal conductivity of disordered metals

Sun, 24 Oct 2004 22:00:00 GMT

Electronic thermal conductivity of disordered metals Raimondi, Roberto; Savona, Giorgio; Schwab, Peter; Luck, Thomas 2004-10-25 Physical Review B-Condensed Matter and Material Physics 70 155109 We calculate the thermal conductivity of interacting electrons in disordered metals. In our analysis we point out that the interaction affects thermal transport through two distinct mechanisms, associated with quantum interference corrections and energy exchange of the quasiparticles with the electromagnetic environment, respectively. The latter is seen to lead to a violation of the Wiedemann-Franz law. Our theory, valid to all orders in perturbation theory, predicts a strong enhancement of the Lorenz ratio κ∕σT over the value predicted by the Wiedemann-Franz law, when the electrons encounter a large environmental impedance.

Spin relaxation in narrow wires of a two-dimensional electron gas

Wed, 18 Oct 2006 22:00:00 GMT

Spin relaxation in narrow wires of a two-dimensional electron gas Schwab, Peter; Dzierzawa, Michael; Gorini, Cosimo; Raimondi, Roberto 2006-10-19 Physical Review B-Condensed Matter and Material Physics 74 155316 How does an initially homogeneous spin polarization in a confined two-dimensional electron gas with Rashba spin-orbit coupling evolve in time? How does the relaxation time depend on system size? We study these questions for systems of a size that is much larger than the Fermi wavelength, but comparable and even shorter than the spin relaxation length. Depending on the confinement spin relaxation may become faster or slower than in the bulk. An initially homogeneously polarized spin system evolves into a spiral pattern.

Magneto-spin Hall conductivity of a two-dimensional electron gas

Thu, 05 Jun 2008 08:13:23 GMT

Magneto-spin Hall conductivity of a two-dimensional electron gas Milletarì, Mirco; Raimondi, Roberto; Schwab, Peter 2008-06-05T08:13:23Z Europhysics Letters 82 67005 It is shown that the interplay of long-range disorder and in-plane magnetic field gives rise to an out-of-plane spin polarization and a finite spin Hall conductivity of the two-dimensional electron gas in the presence of Rashba spin-orbit coupling. A key aspect is provided by the electric-field–induced in-plane spin polarization. Our results are obtained first in the clean limit where the spin-orbit splitting is much larger than the disorder broadening of the energy levels via the diagrammatic evaluation of the Kubo formula. Then the results are shown to hold in the full range of the disorder parameter αpFτ by means of the quasiclassical Green function technique.

Spin-Hall effect in a disordered two-dimensional electron system

Sun, 23 Jan 2005 23:00:00 GMT

Spin-Hall effect in a disordered two-dimensional electron system Raimondi, Roberto; Schwab, Peter 2005-01-24 Physical Review B-Condensed Matter and Material Physics 71 033311 We calculate the spin-Hall conductivity for a two-dimensional electron gas within the self-consistent Born approximation, varying the strength and type of disorder. In the weak disorder limit we find both analytically and numerically a vanishing spin-Hall conductivity even when we allow a momentum dependent scattering. Separating the reactive from the dissipative current response, we find the universal value = e/8 for the reactive response, which cancels however with the dissipative part = –e/8.

Quasiclassical theory of charge transport in disordered interacting electron systems

Sun, 12 Oct 2003 22:00:00 GMT

Quasiclassical theory of charge transport in disordered interacting electron systems Schwab, Peter; Raimondi, Roberto 2003-10-13 Annalen der Physik 12 471-516 We consider the corrections to the Boltzmann theory of electrical transport arising from the Coulomb interaction in disordered conductors. In this article the theory is formulated in terms of quasiclassical Green's functions. We demonstrate that the formalism is equivalent to the conventional diagrammatic technique by deriving the well-known Altshuler-Aronov corrections to the conductivity. Compared to the conventional approach, the quasiclassical theory has the advantage of being closer to the Boltzmann theory, and also allows description of interaction effects in the transport across interfaces, as well as non-equilibrium phenomena in the same theoretical framework. As an example, by applying the Zaitsev boundary conditions which were originally developed for superconductors, we obtain the P(E)-theory of the Coulomb blockade in tunnel junctions. Furthermore we summarize recent results obtained for the non-equilibrium transport in thin films, wires and fully coherent conductors.

Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities

Sun, 28 Sep 2008 22:00:00 GMT

Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities Gorini, Cosimo; Schwab, Peter; Dzierzawa, Michael; Raimondi, Roberto 2008-09-29 Physical Review B-Condensed Matter and Material Physics 78 125327 We consider a two-dimensional electron gas in the presence of Rashba spin-orbit coupling, and study the effects of magnetic s-wave and long-range nonmagnetic impurities on the spin-charge dynamics of the system. We focus on voltage induced spin polarizations and their relation to spin Hall currents. Our results are obtained using the quasiclassical Green function technique, and hold in the full range of the disorder parameter αpF.

Spin Hall effect in a 2DEG in the presence of magnetic couplings

Sat, 31 Jan 2009 23:00:00 GMT

Spin Hall effect in a 2DEG in the presence of magnetic couplings Gorini, Cosimo; Schwab, Peter; Dzierzawa, Michael; Raimondi, Roberto; Milletarì, Mirco 2009-02 1-4 It is now well established that the peculiar linear-in-momentum dependence of the Rashba (and of the Dresselhaus) spin-orbit coupling leads to the vanishing of the spin Hall conductivity in the bulk of a two-dimensional electron gas (2DEG). In this paper we discuss how generic magnetic couplings change this behaviour providing then a potential handle on the spin Hall effect. In particular we examine the influence of magnetic impurities and an in-plane magnetic field. We find that in both cases there is a finite spin Hall effect and we provide explicit expressions for the spin Hall conductivity. The results can be obtained by means of the quasiclassical Green function approach, that we have recently extended to spin-orbit coupled electron systems.