7,337 research outputs found
Hirota equation as an example of integrable symplectic map
The hamiltonian formalism is developed for the sine-Gordon model on the
space-time light-like lattice, first introduced by Hirota. The evolution
operator is explicitely constructed in the quantum variant of the model, the
integrability of the corresponding classical finite-dimensional system is
established.Comment: 10 pages, LaTe
Total Polarisation Conversion in Two-dimensional Electron System under Cyclotron Resonance Conditions
The polarisation conversion of a linear polarised electromagnetic wave
incident onto a two-dimensional (2D) electron system at an angle is
theoretically studied. We consider the 2D system located at the interface
between two dielectric media with different dielectric constants. An external
dc magnetic field is assumed to be directed along the normal to the 2D electron
layer. In such a configuration the cyclotron-polaritons (CPs) in 2D electron
system can be excited with the frequencies in the vicinity of the cyclotron
frequency. Under the CPs excitation the resonance polarisation conversion of
electromagnetic wave greatly increases in the system. In the absence of the
electron scattering in 2D system, the polarisation conversion reaches 100% at a
certain value of the angle of incidence which is more than the total reflection
angle. Extremely high polarisation conversion takes place in a quite wide range
of variation of the angle of incidence. High polarisation conversion efficiency
(above 80%) remains when the actual electron scattering in the 2D system on
GsAs is taken into account. The considered phenomena may be taken up in
polarisation spectroscopy of 2D electron systems.Comment: 7 pages, 5 Postscript figure
Topological Insulators with Inversion Symmetry
Topological insulators are materials with a bulk excitation gap generated by
the spin orbit interaction, and which are different from conventional
insulators. This distinction is characterized by Z_2 topological invariants,
which characterize the groundstate. In two dimensions there is a single Z_2
invariant which distinguishes the ordinary insulator from the quantum spin Hall
phase. In three dimensions there are four Z_2 invariants, which distinguish the
ordinary insulator from "weak" and "strong" topological insulators. These
phases are characterized by the presence of gapless surface (or edge) states.
In the 2D quantum spin Hall phase and the 3D strong topological insulator these
states are robust and are insensitive to weak disorder and interactions. In
this paper we show that the presence of inversion symmetry greatly simplifies
the problem of evaluating the Z_2 invariants. We show that the invariants can
be determined from the knowledge of the parity of the occupied Bloch
wavefunctions at the time reversal invariant points in the Brillouin zone.
Using this approach, we predict a number of specific materials are strong
topological insulators, including the semiconducting alloy Bi_{1-x} Sb_x as
well as \alpha-Sn and HgTe under uniaxial strain. This paper also includes an
expanded discussion of our formulation of the topological insulators in both
two and three dimensions, as well as implications for experiments.Comment: 16 pages, 7 figures; published versio
Twistorial versus space--time formulations: unification of various string models
We introduce the D=4 twistorial tensionfull bosonic string by considering the
canonical twistorial 2--form in two--twistor space. We demonstrate its
equivalence to two bosonic string models: due to Siegel (with covariant
worldsheet vectorial string momenta ) and the one with
tensorial string momenta . We show how to obtain in
mixed space-time--twistor formulation the Soroka--Sorokin--Tkach--Volkov (SSTV)
string model and subsequently by harmonic gauge fixing the Bandos--Zheltukhin
(BZ) model, with constrained spinorial coordinates.Comment: RevTex4,APS, 4 pages. The version which appears in Phys. Rev.
Spin-polarized Josephson and quasiparticle currents in superconducting spin-filter tunnel junctions
We present a theoretical study of the effect of spin-filtering on the
Josephson and dissipative quasiparticle currents in a superconducting tunnel
junction. By combining the quasiclassical Green's functions and the tunneling
Hamiltonian method we describe the transport properties of a generic junction
consisting of two superconducting leads with an effective exchange field h
separated by a spin-filter insulating barrier. We show that besides the
tunneling of Cooper pairs with total spin-projection Sz = 0 there is another
contribution to the Josephson current due to equal-spin Cooper pairs. The
latter is finite and not affected by the spin-filter effect provided that the
fields h and the magnetization of the barrier are non-collinear . We also
determine the quasiparticle current for a symmetric junction and show that the
differential conductance may exhibit peaks at different values of the voltage
depending on the polarization of the spin-filter, and the relative angle
between the exchange fields and the magnetization of the barrier. Our findings
provide a plausible explanation for existing experiments on Josephson junctions
with magnetic barriers, predict new effects and show how spin-polarized
supercurrents in hybrid structures can be created.Comment: 5 pages; 3 figure
Spin-Orbit Interactions in Bilayer Exciton-Condensate Ferromagnets
Bilayer electron-hole systems with unequal electron and hole densities are
expected to have exciton condensate ground states with spontaneous
spin-polarization in both conduction and valence bands. In the absence of
spin-orbit and electron-hole exchange interactions there is no coupling between
the spin-orientations in the two quantum wells. In this article we show that
Rashba spin-orbit interactions lead to unconventional magnetic anisotropies,
whose strength we estimate, and to ordered states with unusual quasiparticle
spectra.Comment: 36 pages, 12 figure
DMRG and the Two Dimensional t-J Model
We describe in detail the application of the recent non-Abelian Density
Matrix Renormalization Group (DMRG) algorithm to the two dimensional t-J model.
This extension of the DMRG algorithm allows us to keep the equivalent of twice
as many basis states as the conventional DMRG algorithm for the same amount of
computational effort, which permits a deeper understanding of the nature of the
ground state.Comment: 16 pages, 3 figures. Contributed to the 2nd International Summer
School on Strongly Correlated Systems, Debrecen, Hungary, Sept. 200
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