833 research outputs found
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
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
Spin orbit coupling in bulk ZnO and GaN
Using group theory and Kane-like model together with the
L\"owdining partition method, we derive the expressions of spin-orbit coupling
of electrons and holes, including the linear- Rashba term due to the
intrinsic structure inversion asymmetry and the cubic- Dresselhaus term due
to the bulk inversion asymmetry in wurtzite semiconductors. The coefficients of
the electron and hole Dresselhaus terms of ZnO and GaN in wurtzite structure
and GaN in zinc-blende structure are calculated using the nearest-neighbor
and tight-binding models separately.Comment: 9 pages, 6 figures, to be published in J. Appl. Phy
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
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
Hole spin relaxation in -type (111) GaAs quantum wells
Hole spin relaxation in -type (111) GaAs quantum wells is investigated in
the case with only the lowest hole subband, which is heavy-hole like in (111)
GaAs/AlAs and light-hole like in (111) GaAs/InP quantum wells, being relevant.
The subband L\"{o}wdin perturbation method is applied to obtain the effective
Hamiltonian including the Dresselhaus and Rashba spin-orbit couplings. Under a
proper gate voltage, the total in-plane effective magnetic field in (111)
GaAs/AlAs quantum wells can be strongly suppressed in the whole momentum space,
while the one in (111) GaAs/InP quantum wells can be suppressed only on a
special momentum circle. The hole spin relaxation due to the D'yakonov-Perel'
and Elliott-Yafet mechanisms is calculated by means of the fully microscopic
kinetic spin Bloch equation approach with all the relevant scatterings
explicitly included. For (111) GaAs/AlAs quantum wells, extremely long
heavy-hole spin relaxation time (upto hundreds of nanoseconds) is predicted. In
addition, we predict a pronounced peak in the gate-voltage dependence of the
heavy-hole spin relaxation time due to the D'yakonov-Perel' mechanism. This
peak origins from the suppression of the unique inhomogeneous broadening in
(111) GaAs/AlAs quantum wells. Moreover, the Elliott-Yafet mechanism influences
the spin relaxation only around the peak area due to the small spin mixing
between the heavy and light holes in quantum wells with small well width. We
also show the anisotropy of the spin relaxation. In (111) GaAs/InP quantum
wells, a mild peak, similar to the case for electrons in (111) GaAs quantum
wells, is also predicted in the gate-voltage dependence of the light-hole spin
relaxation time. The contribution of the Elliott-Yafet mechanism is always
negligible in this case.Comment: 9 pages, 4 figure
Detection of large magneto-anisotropy of electron spin dephasing in a high-mobility two-dimensional electron system in a GaAs/AlGaAs quantum well
In time-resolved Faraday rotation experiments we have detected an inplane
anisotropy of the electron spin-dephasing time (SDT) in an
--modulation-doped GaAs/AlGaAs single quantum well. The SDT
was measured with magnetic fields of T, applied in the and
inplane crystal directions of the GaAs quantum well. For fields
along , we have found an up to a factor of about 2 larger SDT than
in the perpendicular direction. Fully microscopic calculations, by numerically
solving the kinetic spin Bloch equations considering the D'yakonov-Perel' and
the Bir-Aronov-Pikus mechanisms, reproduce the experimental findings
quantitatively. This quantitative analysis of the data allowed us to determine
the relative strengths of Rashba and Dresselhaus terms in our sample. Moreover,
we could estimate the SDT for spins aligned in the {\em inplane}
direction to be on the order of several nanoseconds, which is up to two orders
of magnitude larger than that in the perpendicular {\em inplane} direction.Comment: 4 pages, 4 figures, to be published in PR
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