487 research outputs found
Spin relaxation and anticrossing in quantum dots: Rashba versus Dresselhaus spin-orbit coupling
The spin-orbit splitting of the electron levels in a two-dimensional quantum
dot in a perpendicular magnetic field is studied. It is shown that at the point
of an accidental degeneracy of the two lowest levels above the ground state the
Rashba spin-orbit coupling leads to a level anticrossing and to mixing of
spin-up and spin-down states, whereas there is no mixing of these levels due to
the Dresselhaus term. We calculate the relaxation and decoherence times of the
three lowest levels due to phonons. We find that the spin relaxation rate as a
function of a magnetic field exhibits a cusp-like structure for Rashba but not
for Dresselhaus spin-orbit interaction.Comment: 6 pages, 1 figur
Interacting fermions in two dimensions: beyond the perturbation theory
We consider a system of 2D fermions with short-range interaction. A
straightforward perturbation theory is shown to be ill-defined even for an
infinitesimally weak interaction, as the perturbative series for the
self-energy diverges near the mass shell. We show that the divergences result
from the interaction of fermions with the zero-sound collective mode. By
re-summing the most divergent diagrams, we obtain a closed form of the
self-energy near the mass shell. The spectral function exhibits a threshold
feature at the onset of the emission of the zero-sound waves. We also show that
the interaction with the zero sound does not affect a non-analytic,
-part of the specific heat.Comment: 5 pages, 4 figure
Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates
A theoretical prediction of the spin-dependent electron self-energy and
in-plane transport of a two-dimensional electron gas in proximity with a
ferromagnetic gate is presented. The application of the predicted
spin-dependent properties is illustrated by the proposal of a device
configuration with two neighboring ferromagnetic gates which produces a
magnetoresistance effect on the channel current generated by nonmagnetic source
and drain contacts. Specific results are shown for a silicon inversion layer
with iron gates. The gate leakage current is found to be beneficial to the spin
effects.Comment: 3 pages, 2 figures, Replaced with revised versio
Electron spin-orbit splitting in InGaAs/InP quantum well studied by means of the weak antilocalization and spin-zero effects in tilted magnetic fields
The coupling between Zeeman spin splitting and Rashba spin-orbit terms has
been studied experimentally in a gated InGaAs/InP quantum well structure by
means of simultaneous measurements of the weak antilocalization (WAL) effect
and beating in the SdH oscillations. The strength of the Zeeman splitting was
regulated by tilting the magnetic field with the spin-zeros in the SdH
oscillations, which are not always present, being enhanced by the tilt. In
tilted fields the spin-orbit and Zeeman splittings are not additive, and a
simple expression is given for the energy levels. The Rashba parameter and the
electron g-factor were extracted from the position of the spin zeros in tilted
fields. A good agreement is obtained for the spin-orbit coupling strength from
the spin-zeros and weak antilocalization measurements.Comment: Accepted for publication in Semiconductors Science and Technolog
Mixing of two-electron spin states in a semiconductor quantum dot
We show that the low lying spin states of two electrons in a semiconductor
quantum dot can be strongly mixed by electron-electron asymmetric exchange.
This mixing is generated by the coupling of electron spin to its orbital motion
and to the relative orbital motion of the two electrons. The asymmetric
exchange can be as large as 50% of the isotropic exchange, even for cylindrical
quantum dots. The resulting spin mixing contributes to understanding spin
dynamics in quantum dots, including light polarization reversal
Massive Spin Collective Mode in Quantum Hall Ferromagnet
It is shown that the collective spin rotation of a single Skyrmion in quantum
Hall ferromagnet can be regarded as precession of the entire spin texture in
the external magnetic field, with an effective moment of inertia which becomes
infinite in the zero g-factor limit. This low-lying spin excitation may
dramatically enhance the nuclear spin relaxation rate via the hyperfine
interaction in the quantum well slightly away from filling factor equal one.Comment: 4 page
Anomalous Hall effect in a two-dimensional electron gas with spin-orbit interaction
We discuss the mechanism of anomalous Hall effect related to the contribution
of electron states below the Fermi surface (induced by the Berry phase in
momentum space). Our main calculations are made within a model of
two-dimensional electron gas with spin-orbit interaction of the Rashba type,
taking into account the scattering from impurities. We demonstrate that such an
"intrinsic" mechanism can dominate but there is a competition with the
impurity-scattering mechanism, related to the contribution of states in the
vicinity of Fermi surface. We also show that the contribution to the Hall
conductivity from electron states close to the Fermi surface has the intrinsic
properties as well.Comment: 9 pages, 6 figure
Quasi-ballistic transport in HgTe quantum-well nanostructures
The transport properties of micrometer scale structures fabricated from
high-mobility HgTe quantum-wells have been investigated. A special photoresist
and Ti masks were used, which allow for the fabrication of devices with
characteristic dimensions down to 0.45 m. Evidence that the transport
properties are dominated by ballistic effects in these structures is presented.
Monte Carlo simulations of semi-classical electron trajectories show good
agreement with the experiment.Comment: 3 pages, 3 figures; minor revisions: replaced "inelastic mean free
path" with "transport mean free path"; corrected typing errors; restructered
most paragraphs for easier reading; accepted for publication in AP
Absence of weak antilocalization in ferromagnetic films
We present magnetoresistance measurements performed on ultrathin films of
amorphous Ni and Fe. In these films the Curie temperature drops to zero at
small thickness, making it possible to study the effect of ferromagnetism on
localization. We find that non-ferromagnetic films are characterized by
positive magnetoresistance. This is interpreted as resulting from weak
antilocalization due to strong Bychkov-Rashba spin orbit scattering. As the
films become ferromagnetic the magnetoresistance changes sign and becomes
negative. We analyze our data to identify the individual contributions of weak
localization, weak antilocalization and anisotropic magnetoresistance and
conclude that the magnetic order suppresses the influence of spin-orbit effects
on localization phenomena in agreement with theoretical predictions.Comment: 6 pages, 6 figure
Spin precession due to spin-orbit coupling in a two-dimensional electron gas with spin injection via ideal quantum point contact
We present the analytical result of the expectation value of spin resulting
from an injected spin polarized electron into a semi-infinitely extended 2DEG
plane with [001] growth geometry via ideal quantum point contact. Both the
Rashba and Dresselhaus spin-orbit couplings are taken into account. A pictorial
interpretation of the spin precession along certain transport directions is
given. The spin precession due to the Rashba term is found to be especially
interesting since it behaves simply like a windshield wiper which is very
different from the ordinary precession while that due to the Dresselhaus term
is shown to be crystallographic-direction-dependent. Some crystallographic
directions with interesting and handleable behavior of spin precession are
found and may imply certain applicability in spintronic devices.Comment: 5 pages, 2 figures, submitted to Phys. Rev.
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