1,038 research outputs found
Gauge covariant formulation of Wigner representation through deformational quantization --Application to Keldysh formalism with electromagnetic field--
We developed a gauge-covariant formulation of the non-equilibrium Green
function method for the dynamical and/or non-uniform electromagnetic field by
means of the deformational quantization method. Such a formulation is realized
by replacing the Moyal product in the so-called Wigner space by the star
product, and facilitates the order-by-order calculation of a gauge-invariant
observable in terms of the electromagnetic field. An application of this
formalism to the linear response theory is discussed
Quantum Tunneling in Half-Integer Spin Systems
Motivated by the experimental observations of resonant tunnelings in the
systems with half-integer spin, such as V and Mn, we study the
mechanism of adiabatic change of the magnetization in systems with the
time-reversal symmetry. Within the time-reversal symmetric models, effects of
several types of perturbations are investigated. Although tunneling between the
ground states is suppressed in a simple Kramers doublet, we show that the
nonadiabatic transition governed by the Landau-Zener-St\"uckelberg mechanism
occurs in many cases due to the additional degeneracy of the ground state. We
also found more general cases where LZS mechanism can not be applied directly
even the system shows a kind of adiabatic change of the magnetization
Anomalous Nernst and Hall effects in magnetized platinum and palladium
We study the anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in
proximity-induced ferromagnetic palladium and platinum which is widely used in
spintronics, within the Berry phase formalism based on the relativistic band
structure calculations. We find that both the anomalous Hall ()
and Nernst () conductivities can be related to the spin Hall
conductivity () and band exchange-splitting () by
relations and
,
respectively. In particular, these relations would predict that the
in the magnetized Pt (Pd) would be positive (negative) since
the is positive (negative). Furthermore, both
and are approximately proportional to the
induced spin magnetic moment () because the is a linear
function of . Using the reported in the magnetized Pt and Pd, we
predict that the intrinsic anomalous Nernst conductivity (ANC) in the magnetic
platinum and palladium would be gigantic, being up to ten times larger than,
e.g., iron, while the intrinsic anomalous Hall conductivity (AHC) would also be
significant.Comment: Accepted for publication in the Physical Review
Conductance through a Magnetic Domain Wall in Double Exchange System
The conductance through a magnetic domain wall is calculated for the double
exchange system as a function of energy and the width of the domain wall. It is
shown that when the carrier density is low enough, the blockade is almost
complete even for the smoothly varying spin configuration, i.e., large width of
the domain wall. This result is applied to the manganese oxides.Comment: 3 pages, LaTex, 1 Postscript figur
Photo-induced insulator-metal transition of a spin-electron coupled system
The photo-induced metal-insulator transition is studied by the numerical
simulation of real-time quantum dynamics of a double-exchange model. The
spatial and temporal evolutions of the system during the transition have been
revealed including (i) the threshold behavior with respect to the intensity and
energy of light, (ii) multiplication of particle-hole (p-h) pairs by a p-h pair
of high energy, and (iii) the space-time pattern formation such as (a) the
stripe controlled by the polarization of light, (b) coexistence of metallic and
insulating domains, and (c) dynamical spontaneous symmetry-breaking associated
with the spin spiral formation imposed by the conservation of total spin for
small energy-dissipation rates
Josephson and proximity effects on the surface of a topological insulator
We investigate Josephson and proximity effects on the surface of a
topological insulator on which superconductors and a ferromagnet are deposited.
The superconducting regions are described by the conventional BCS Hamiltonian,
rather than the superconducting Dirac Hamiltonian. Junction interfaces are
assumed to be dirty. We obtain analytical expressions of the Josephson current
and the proximity-induced anomalous Green's function on the topological
insulator. The dependence of the Josephson effect on the junction length, the
temperature, the chemical potential and the magnetization is discussed. It is
also shown that the proximity-induced pairing on the surface of a topological
insulator includes even and odd frequency triplet pairings as well as a
conventional s-wave one.Comment: 7 pages, 5 figure
Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets
In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in and
compounds.Comment: Latex fil
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