121 research outputs found
Effective g-factor tensor for carriers in IV-VI semiconductor quantum wells
A theory for the electron (and hole) g factor in multivalley lead-salt IV-VI semiconductor quantum wells (QWs) is presented. An effective Hamiltonian for theQWelectronic states in the presence of an external magnetic field is introduced within the envelope-function approximation, based on the multiband kp Dimmock model for the bulk. The mesoscopic spin-orbit (Rashba-type) and Zeeman interactions are taken into account on an equal footing and the effective g factor in symmetric quantum wells (g*(QW)) is calculated analytically for each nonequivalent conduction-band (and valence-band) valley, and for QWs grown along different crystallographic directions
Spin-dependent resonant tunneling in semiconductor nanostructures
The spin-dependent quantum transport of electrons in non magnetic III-V semiconductor nanos-tructures is studied theoretically within the envelope function approximation and the Kane model for the bulk. It is shown that an unpolarized beam of conducting electrons can be strongly polarized in zero magnetic field by resonant tunneling across asymmetric double-barrier structures, as an effect of the spin-orbit interaction. The electron transmission probability is calculated as a function of energy and angle of incidence. Specific results for tunneling across lattice matched politype Ga0.47In0.53As / InP/Ga0.47In0.53As / GaAs0.5Sb0.5 / Ga0.47In0.53 As double barrier heterostructures show sharp spin split resonances, corresponding to resonant tunneling through spin-orbit split quasi-bound electron states. The polarization of the transmitted beam is also calculated and is shown to be over 50%
Topological Dirac states in asymmetric Pb1-xSnxTe quantum wells
The electronic structure of lead-salt (IV-VI semiconductor) topological
quantum wells (T-QWs) is investigated with analytical solutions of the
effective 4x4 Dimmock k & BULL; p model, which gives an accurate
description of the bands around the fundamental energy gap. Specific
results for three-layer Pb1-xSnxTe nanostructures with varying Sn
composition are presented and the main differences between topological
and normal (N) QWs highlighted. A series of new features are found in
the spectrum of T-QWs, in particular in asymmetric QWs where large
(Rashba spin-orbit) splittings are obtained for the topological Dirac
states inside the gap
Electron g factor anisotropy in asymmetric III-V semiconductor quantum wells
The electron effective g factor tensor in asymmetric III-V semiconductor quantum wells (AQWs) and its tuning with the structure parameters and composition are investigated with envelope-function theory and the 8 x 8k . p Kane model. The spin-dependent terms in the electron effective Hamiltonian in the presence of an external magnetic field are treated as a perturbation and the g factors g(perpendicular to)* and g(parallel to)*, for the magnetic field in the QW plane and along the growth direction, are obtained analytically as a function of the well width L. The effects of the structure inversion asymmetry (SIA) on the electron g factor are analyzed. For the g-factor main anisotropy Delta g = g(perpendicular to)*-g(parallel to)*. in AQWs, a sign change is predicted in the narrow well limit due to SIA, which can explain recent measurements and be useful in spintronic applications. Specific results for narrow-gap AlSb/InAs/GaSb and AlxGa1-xAsGaAs/AlyGa1-yAs AQWs are presented and discussed with the available experimental data; in particular InAs QWs are shown to not only present much larger g factors but also a larger g-factor anisotropy, and with the opposite sign with respect to GaAs QWs
Weak localization and spin splitting in inversion layers on p-type InAs
We report on the magnetoconductivity of quasi two-dimensional electron
systems in inversion layers on p-type InAs single crystals. In low magnetic
fields pronounced features of weak localization and antilocalization are
observed. They are almost perfectly described by the theory of Iordanskii,
Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the
Rashba parameter of the ground electric subband as a function of the electron
density.Comment: Accepted for publication in Phys. Rev. B, 4 page
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
Rashba spin-orbit coupling and spin relaxation in silicon quantum wells
Silicon is a leading candidate material for spin-based devices, and
two-dimensional electron gases (2DEGs) formed in silicon heterostructures have
been proposed for both spin transport and quantum dot quantum computing
applications. The key parameter for these applications is the spin relaxation
time. Here we apply the theory of D'yakonov and Perel' (DP) to calculate the
electron spin resonance linewidth of a silicon 2DEG due to structural inversion
asymmetry for arbitrary static magnetic field direction at low temperatures. We
estimate the Rashba spin-orbit coupling coefficient in silicon quantum wells
and find the and times of the spins from this mechanism as a
function of momentum scattering time, magnetic field, and device-specific
parameters. We obtain agreement with existing data for the angular dependence
of the relaxation times and show that the magnitudes are consistent with the DP
mechanism. We suggest how to increase the relaxation times by appropriate
device design.Comment: Extended derivations and info, fixed typos and refs, updated figs and
data. Worth a re-downloa
Shot noise and spin-orbit coherent control of entangled and spin polarized electrons
We extend our previous work on shot noise for entangled and spin polarized
electrons in a beam-splitter geometry with spin-orbit (\textit{s-o})
interaction in one of the incoming leads (lead 1). Besides accounting for both
the Dresselhaus and the Rashba spin-orbit terms, we present general formulas
for the shot noise of singlet and triplets states derived within the scattering
approach. We determine the full scattering matrix of the system for the case of
leads with \textit{two} orbital channels coupled via weak \textit{s-o}
interactions inducing channel anticrossings. We show that this interband
coupling coherently transfers electrons between the channels and gives rise to
an additional modulation angle -- dependent on both the Rashba and Dresselhaus
interaction strengths -- which allows for further independent coherent control
of the electrons traversing the incoming leads. We derive explicit shot noise
formulas for a variety of correlated pairs (e.g., Bell states) and lead spin
polarizations. Interestingly, the singlet and \textit{each} of the triplets
defined along the quantization axis perpendicular to lead 1 (with the local
\textit{s-o} interaction) and in the plane of the beam splitter display
distinctive shot noise for injection energies near the channel anticrossings;
hence, one can tell apart all the triplets, in addition to the singlet, through
noise measurements. We also find that spin-orbit induced backscattering within
lead 1 reduces the visibility of the noise oscillations, due to the additional
partition noise in this lead. Finally, we consider injection of two-particle
wavepackets into leads with multiple discrete states and find that two-particle
entanglement can still be observed via noise bunching and antibunching.Comment: 30 two-column pages and 7 figure
Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry
In semiconductor heterostructures, bulk and structural inversion asymmetry
and spin-orbit coupling induce a k-dependent spin splitting of valence and
conduction subbands, which can be viewed as being caused by momentum-dependent
crystal magnetic fields. This paper studies the influence of these effective
magnetic fields on the intersubband spin dynamics in an asymmetric n-type
GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin
plasmons using linear response theory. The so-called D'yakonov-Perel'
decoherence mechanism is inactive for collective intersubband excitations,
i.e., crystal magnetic fields do not lead to decoherence of spin plasmons.
Instead, we predict that the main signature of bulk and structural inversion
asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting
of the spin plasmon dispersion. The importance of many-body effects is pointed
out, and conditions for experimental observation with inelastic light
scattering are discussed.Comment: 8 pages, 6 figure
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