217 research outputs found
Hysteresis effect due to the exchange Coulomb interaction in short-period superlattices in tilted magnetic fields
We calculate the ground-state of a two-dimensional electron gas in a
short-period lateral potential in magnetic field, with the Coulomb
electron-electron interaction included in the Hartree-Fock approximation. For a
sufficiently short period the dominant Coulomb effects are determined by the
exchange interaction. We find numerical solutions of the self-consistent
equations that have hysteresis properties when the magnetic field is tilted and
increased, such that the perpendicular component is always constant. This
behavior is a result of the interplay of the exchange interaction with the
energy dispersion and the spin splitting. We suggest that hysteresis effects of
this type could be observable in magneto-transport and magnetization
experiments on quantum-wire and quantum-dot superlattices.Comment: 3 pages, 3 figures, Revtex, to appear in Phys. Rev.
Non-adiabatic generation of a pure spin current in a 1D quantum ring with spin-orbit interaction
We demonstrate the theoretical possibility of obtaining a pure spin current
in a 1D ring with spin-orbit interaction by irradiation with a non-adiabatic,
two-component terahertz laser pulse, whose spatial asymmetry is reflected by an
internal dephasing angle . The stationary solutions of the equation of
motion for the density operator are obtained for a spin-orbit coupling linear
in the electron momentum (Rashba) and used to calculate the time-dependent
charge and spin currents. We find that there are critical values of at
which the charge current disappears, while the spin current reaches a maximum
or a minimum value.Comment: 8 pages, 5 figure
Weak Localization in a Lateral Superlattice with Rashba and Dresselhaus Spin-Orbit Interaction
We calculate the weak localization (WL) correction to the conductivity of a lateral superlattice (LSL) with Rashba (R)-Dresselhaus (D) spin-orbit interaction (SOI). The superlattice is modeled as a sequence of parallel wires that support tunneling between adjacent sites, leading to the formation of extended Bloch states along its axis and a miniband in the energy spectrum. Our results, obtained by calculating the eigenvalues of the Cooperon operator in the diffusion approximation, indicate that the electron dephasing rate that determines the antilocalization correction is enhanced by a term proportional with the LSL potential and the bandwidth. Within the same formalism, the spin-relaxation rates associated with the localization corrections are found to exhibit a strong anisotropy dictated by the relative strength of the two SOI couplings, as well as by the orientation of the LSL axis
Generalized Master equation approach to mesoscopic time-dependent transport
We use a generalized Master equation (GME) formalism to describe the
non-equilibrium time-dependent transport through a short quantum wire connected
to semi-infinite biased leads. The contact strength between the leads and the
wire are modulated by out-of-phase time-dependent functions which simulate a
turnstile device. One lead is fixed at one end of the sample whereas the other
lead has a variable placement. The system is described by a lattice model. We
find that the currents in both leads depend on the placement of the second
lead. In the rather small bias regime we obtain transient currents flowing
against the bias for short time intervals. The GME is solved numerically in
small time steps without resorting to the traditional Markov and rotating wave
approximations. The Coulomb interaction between the electrons in the sample is
included via the exact diagonalization method
Non-adiabatic Current Excitation in Quantum Rings
We investigate the difference in the response of a one-dimensional
semiconductor quantum ring and a finite-width ring to a strong and short-lived
time-dependent perturbation in the THz regime. In both cases the persistent
current is modified through a nonadiabatic change of the many-electron states
of the system, but by different mechanisms in each case.Comment: LaTeX, 5 pages with 6 embedded postscript figures, submitted to 20th
Nordic Semiconductor Meeting, Tampere (2003
Nonadiabatic generation of spin currents in a quantum ring with Rashba and Dresselhaus spin-orbit interactions
When subjected to a linearly polarized terahertz pulse, a mesoscopic ring
endowed with spin-orbit interaction (SOI) of the Rashba-Dresselhaus type
exhibits nonuniform azimuthal charge and spin distributions. Both types of SOI
couplings are considered linear in the electron momentum. Our results are
obtained within a formalism based on the equation of motion satisfied by the
density operator which is solved numerically for different values of the angle
, the angle determining the polarization direction of the laser pulse.
Solutions thus obtained are later employed in determining the time-dependent
charge and spin currents, whose values are calculated in the stationary limit.
Both these currents exhibit an oscillatory behavior complicated in the case of
the spin current by a beating pattern. We explain this occurrence on account of
the two spin-orbit interactions which force the electron spin to oscillate
between the two spin quantization axes corresponding to Rashba and Dresselhaus
interactions. The oscillation frequencies are explained using the single
particle spectrum.Comment: 9 pages, 5 figures, Conference "Advanced many-body and statistical
methods in mesoscopic systems", June 27 -July 2, 2011, Constanta, Romani
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