21 research outputs found
Spin-orbit terms in multi-subband electron systems: A bridge between bulk and two-dimensional Hamiltonians
This a preprint of the materials accepted for publication in Semiconductors Copyright © 2008 SP MAIK Nauka/Interperiodica / SpringerWe analyze the spin-orbit terms in multi-subband quasi-two-dimensional electron systems, and how they descend from the bulk Hamiltonian of the conduction band. Measurements of spin-orbit terms in one subband alone are shown to give incomplete information on the spin-orbit Hamiltonian of the system. They should be complemented by measurements of inter-subband spin-orbit matrix elements. Tuning electron energy levels with a quantizing magnetic field is proposed as an experimental approach to this problem
Probing two-subband systems in a quantizing magnetic field with non-equilibrium phonons
ICPS-26: 26th International Conferences on Physics of Semiconductors, Edinburgh, Scotland, 29 July - 2 August 2002We propose to use phonon absorption spectroscopy to study many-body gaps and phases of two-subband heterostructures in the quantum Hall regime. Implications of the spin-orbit interaction for phonon absorption in this system are considered
Induced currents, frozen charges and the quantum Hall effect breakdown
Puzzling results obtained from torque magnetometry in the quantum Hall effect
(QHE) regime are presented, and a theory is proposed for their explanation.
Magnetic moment saturation, which is usually attributed to the QHE breakdown,
is shown to be related to the charge redistribution across the sample.Comment: 5 pages, 2 figures, Proceedings of the 11th International Symposium
"Nanostructures: Physics and Technology", St.Petersburg, Russia, June 23-28,
2003, expanded version with one figure adde
Spin relaxation and antisymmetric exchange in n-doped III-V semiconductor
Recently K. Kavokin [Phys. Rev. B 64, 075305 (2001)] suggested that the
Dzyaloshinskii-Moriya interaction between localized electrons governs slow spin
relaxation in -doped GaAs in the regime close to the metal-insulator
transition. We derive the correct spin Hamiltonian and apply it to the
determination of spin dephasing time using the method of moments expansion. We
argue that the proposed mechanism is insufficient to explain the observed
values of the spin relaxation time.Comment: 5 pages, 1 figure
Spin-Orbit Coupling and Time-Reversal Symmetry in Quantum Gates
We study the effect of spin-orbit coupling on quantum gates produced by
pulsing the exchange interaction between two single electron quantum dots.
Spin-orbit coupling enters as a small spin precession when electrons tunnel
between dots. For adiabatic pulses the resulting gate is described by a unitary
operator acting on the four-dimensional Hilbert space of two qubits. If the
precession axis is fixed, time-symmetric pulsing constrains the set of possible
gates to those which, when combined with single qubit rotations, can be used in
a simple CNOT construction. Deviations from time-symmetric pulsing spoil this
construction. The effect of time asymmetry is studied by numerically
integrating the Schr\"odinger equation using parameters appropriate for GaAs
quantum dots. Deviations of the implemented gate from the desired form are
shown to be proportional to dimensionless measures of both spin-orbit coupling
and time asymmetry of the pulse.Comment: 10 pages, 3 figure
Low-temperature spin relaxation in n-type GaAs
Low-temperature electron spin relaxation is studied by the optical
orientation method in bulk n-GaAs with donor concentrations from 10^14 cm^{-3}
to 5x10^17 cm^{-3}.
A peculiarity related to the metal-to-insulator transition (MIT) is observed
in the dependence of the spin lifetime on doping near n_D = 2x10^16 cm^{-3}. In
the metallic phase, spin relaxation is governed by the Dyakonov-Perel
mechanism, while in the insulator phase it is due to anisotropic exchange
interaction and hyperfine interactio
Direct Observation of the Electron Spin Relaxation Induced by Nuclei in Quantum Dots
We have studied the electron spin relaxation in semiconductor InAs/GaAs quantum dots by time-resolved optical spectroscopy. The average spin polarization of the electrons in an ensemble of p-doped quantum dots decays down to 1/3 of its initial value with a characteristic time TDelta[approximate]500 ps, which is attributed to the hyperfine interaction with randomly oriented nuclear spins. We show that this efficient electron spin relaxation mechanism can be suppressed by an external magnetic field as small as 100 mT
Temperature dependence of the breakdown of the quantum Hall effect studied by induced currents
Copyright © 2004 The American Physical SocietyWe have developed a model of the high-current breakdown of the integer quantum Hall effect, as measured in contactless experiments using a highly-sensitive torsion balance magnetometer. The model predicts that, for empirically “low-mobility” samples (μ<75 m2 V−1 s−1), the critical current for breakdown should decrease with, and have a linear dependence on, temperature. This prediction is verified experimentally with the addition of a low-temperature saturation of the critical current at a temperature that depends on both sample number density and filling factor. It is shown that this saturation is consistent with quasielastic inter-Landau-level scattering when the maximum electric field in the sample reaches a large enough value. In addition we show how this model can be extended to give qualitative agreement with experiments on high-mobility samples
Entanglement Transfer via XXZ Heisenberg chain with DM Interaction
The role of spin-orbit interaction, arises from the Dzyaloshinski-Moriya
anisotropic antisymmetric interaction, on the entanglement transfer via an
antiferromagnetic XXZ Heisenberg chain is investigated. From symmetrical point
of view, the XXZ Hamiltonian with Dzyaloshinski-Moriya interaction can be
replaced by a modified XXZ Hamiltonian which is defined by a new exchange
coupling constant and rotated Pauli operators. The modified coupling constant
and the angle of rotations are depend on the strength of Dzyaloshinski-Moriya
interaction. In this paper we study the dynamical behavior of the entanglement
propagation through a system which is consist of a pair of maximally entangled
spins coupled to one end of the chain. The calculations are performed for the
ground state and the thermal state of the chain, separately. In both cases the
presence of this anisotropic interaction make our channel more efficient, such
that the speed of transmission and the amount of the entanglement are improved
as this interaction is switched on. We show that for large values of the
strength of this interaction a large family of XXZ chains becomes efficient
quantum channels, for whole values of an isotropy parameter in the region .Comment: 21 pages, 9 figure
Symmetry of anisotropic exchange interactions in semiconductor nanostructures
The symmetry of exchange interaction of charge carriers in semiconductor
nanostructures (quantum wells and quantum dots) is analysed. It is shown that
the exchange Hamiltonian of two particles belonging to the same energy band can
be universally expressed via pseudospin operators of the particles. The
relative strength of the anisotropic exchange interaction is shown to be
independent of the binding energy and the isotropic exchange constant