K. Nomura

Dependence of the intrinsic spin-Hall effect on spin-orbit interaction character

We report on a comparative numerical study of the spin-Hall conductivity in two dimensions for three different spin-orbit interaction models; the standard k-linear Rashba model, the k-cubic Rashba model that describes two-dimensional hole systems, and a modified k-linear Rashba model in which the spin-orbit coupling strength is energy dependent. Numerical finite-size Kubo formula results indicate that the spin-Hall conductivity of the k-linear Rashba model vanishes for frequency much smaller than the scattering rate x7f1 , with first-order relative fluctuations surviving out to large system sizes. For the k-cubic Rashba model case, the spin-Hall conductivity does not depend noticeably on and is finite in the dc limit, in agreement with experiment. For the modified k-linear Rashba model the spin-Hall conductivity is noticeably dependent but approaches a finite value in the dc limit. We discuss these results in the light of a spectral decomposition of the spin-Hall conductivity and associated sum rules, and in relation to a proposed separation of the spin-Hall conductivity into skew-scattering, intrinsic, and interband vertex correction contributions.

Evolution of ν = 1 bilayer quantum Hall ferromagnet

The fractional quantum Hall effect which appears in a two-dimensional electron system in a strong magnetic field exhibits rich strong correlation phenomena. (1) For a decade, a large number of studies have been made on bilayer quantum Hall systems which consist of a pair of two-dimensional electron gases separated by a distance so small as to be comparable to the typical spacing between electrons in the same layer. (2) The characteristic parameters of this system are the filling factor νT = 2πl 2 n, the distance between the layers d, and the interlayer tunneling rateSAS. Here n is the total electron density of the system and l is the magnetic length. This system can be mapped to an equivalent spin-1/2 system by assigning ↑(↓) pseudo spins to electrons in the upper (lower) layer, where the actual electron spins are assumed to be polarized. In this system, various ground states and spectacular ex- citations are realized depending on the parameters. The Coulomb interaction term consists of direct and exchange terms. Because the latter term tends to align the pseudo spins of the electrons, the ground state has a ferromag- netic long range order at νT = 1/q (q odd) when d ≃ 0. At finite layer separation, the direct part of the electron- electron interaction produces a local capacitive charging energy that is minimized when the two layers have equal electron density and cause the easy-plane(XY) type sym- metry in the pseudospin space. The ferromagnetic order corresponds to the spontaneous interlayer phase coher- ence. The simplest Abelian quantum Hall states for the bi- layer systems at νT = 2/(m+n) are described by the two- component generalization of the Laughlin wave function first introduced by Halperin. (3) �m,m,n =

Vibrational anisotropy and quadrupole interactions of Fe substituted onto the Mn site of the charge and orbitally ordered and disordered layered manganites L BaMn 1.96 Fe 0.04 O 5 and L BaMn 1.96 Fe 0.04 O 6 ( L = Y , Gd, Sm, Nd, Pr, and La)

A. I. Rykov, Y. Ueda, K. Nomura, and M. Seto The University of Tokyo, Hongo 7-3-1, 113-8656, Japan, Technology Crystals Laboratory ”Tecrys”, Institutskaya 4/1, 630090, Novosibirsk, Russia, Institute for Solid State Physics, University of Tokyo, 5-1-5, Kashiwanoha, Chiba 277-8581, Japan, Research Reactor Institute, Kyoto University, Noda, Kumatori-machi, Osaka 590-0494, Japan (Dated: March 23, 2009)

Numerical investigation on asymmetric bilayer system at integer filling factor

Abstract Deformation of the easy-axis ferromagnetic state in asymmetric bilayer systems are investigated numerically. Using the exact diagonalization the easy-axis to easy-plane ferromagnetic transition at total filling factor 3 or 4 is investigated. At still higher filling, novel stripe state in which stripes are aligned in the vertical direction occurs. The Hartree–Fock energies of relevant ordered states are calculated and compared.

Strong Quasi-Particle Tunneling Study in the Paired Quantum Hall States

The quasi-particle tunneling phenomena in the paired fractional quantum Hall states are studied. A single point-contact system is first considered. Because of relevancy of the quasi-particle tunneling term, the strong tunneling regime should be investigated. Using the instanton method it is shown that the strong quasi-particle tunneling regime is described as the weak electron tunneling regime effectively. Expanding to the network model the paired quantum Hall liquid to insulator transition is discussed.

Spin Hall effect in a two dimensional spin-orbit coupled semiconductor system

We report the experimental observation of the spin-Hall effect in a 2D hole system with spin-orbit coupling. The 2D hole layer is a part of a p-n junction light-emitting diode with a specially designed coplanar geometry which allows an angle-resolved polarization detection at opposite edges of the 2D hole system. In equilibrium the angular momenta of the spin-orbit split heavy-hole states lie in the plane of the 2D layer. When an electric field is applied across the hole channel, a nonzero out-of-plane component of the angular momentum is detected whose sign depends on the sign of the electric field and is opposite for the two edges. Microscopic quantum transport calculations show only a weak effect of disorder, suggesting that the clean limit spin-Hall conductance description (intrinsic spin-Hall effect) might apply to our system.

Disorder effects in the anomalous Hall effect induced by Berry curvature RID B-5617-2009

We describe the charge transport in ferromagnets with spin orbit coupled Bloch bands by combining the wave-packet evolution equations with the classical Boltzmann equation. This approach can be justified in the limit of smooth disorder potential. Besides the skew scattering contribution, we demonstrate how other effects of disorder appear which are closely linked to the Berry curvature of the Bloch states associated with the wavepacket. We show that, although being of the same order of magnitude as the clean limit Berry curvature contribution, generally disorder corrections depend differently on various parameters and can lead to the sign reversal of the Hall current as the function of the chemical potential in systems with a non-constant Berry curvature in momentum space. Earlier conclusions on the effects of disorder on the anomalous Hall effect depended stricly on the lack of momentum dependence of the Berry curvature in the models studied and generalizations of their findings to other systems with more complicated band structures were unjustified.

NUMERICAL KUBO FORMULA STUDY OF FRICTIONAL DRAG IN THE INTEGER QUANTUM HALL REGIME

We study interlayer frictional drag between two-dimensional electron systems in the strong magnetic field limit by evaluating the weak-coupling Kubo formula for interlayer drag numerically. The key quantity in this theory is the disorder averaged triangle function, a product of three Greens functions of electrons that represents the dc current response of electrons in one layer to charge fluctuations in a remote current-carrying layer. We find that the disorder averaged triangle functions are proportional to the momentum transfer

Edge state transport of separately contacted bilayer systems in the fractional quantum Hall regime

vec{q}

Room-temperature ferromagnetism of sol-gel-synthesized Sn1−x 57FexO2−(Delta) powders

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