246 research outputs found
Giant edge spin accumulation in a symmetric quantum well with two subbands
We have studied the edge spin accumulation in a high mobility two-dimensional
electron gas formed in a symmetric well with two subbands. This study is
strongly motivated by the recent experiment of Hernandez et al. [Phys. Rev. B
{\bf 88}, 161305(R) (2013)] who demonstrated the spin accumulation near the
edges of a bilayer symmetric GaAs structure in contrast to no effect in a
single-layer configuration. The intrinsic mechanism of the spin-orbit
interaction we consider arises from the coupling between two subband states of
opposite parities. We obtain a parametrically large magnitude of the edge spin
density for the two-subband sample as compared to the usual single-subband
structure. We show that the presence of a gap in the system, i.e., the energy
separation between the two subband bottoms, changes drastically the
picture of the edge spin accumulation. Thus one can easily proceed from the
regime of weak spin accumulation to the regime of strong one by varying the
Fermi energy (electron density) and/or . We estimate that by changing
the gap from zero up to K, the magnitude of the effect
changes by three orders of magnitude. This opens up the possibility for the
design of new spintronic devices.Comment: 6 pages, 2 figures, expanded text and added Supplementary Materia
Bare LO-Phonon Peak in THz-Emission Signals: a Dielectric-Function Analysis
We present a normal-mode analysis of coupled photocarrier-phonon dynamics in
Te. We consider a dielectric function which accounts for LO phonons and the
electron-hole gas within the Debye-Huckel model and RPA. Our main finding is
the existence of a bare LO phonon mode in the system even at high carrier
density. This oscillation is an unscreened L- mode arising from ineffective
screening at large wave vectors. This mode is consistent with the bare
LO-phonon peak in recent THz-emission spectra of Te.Comment: 3 pages, 1 figure, Special Issue: Proceedings of the 10th Brazilian
Workshop on Semiconductor Physics, Guaruja/SP, April/200
Subband structure of II-VI modulation-doped magnetic quantum wells
Here we investigate the spin-dependent subband structure of newly-developed
Mn-based modulation-doped quantum wells. In the presence of an external
magnetic field, the s-d exchange coupling between carriers and localized d
electrons of the Mn impurities gives rise to large spin splittings resulting in
a magnetic-field dependent subband structure. Within the framework of the
effective-mass approximation, we self-consistently calculate the subband
structure at zero temperature using Density Functional Theory (DFT) with a
Local Spin Density Approximation (LSDA). We present results for the
magnetic-field dependence of the subband structure of shallow ZnSe/ZnCdMnSe
modulation doped quantum wells. Our results show a significant contribution to
the self-consistent potential due to the exchange-correlation term. These
calculations are the first step in the study of a variety of interesting
spin-dependent phenomena, e.g., spin-resolved transport and many-body effects
in polarized two-dimensional electron gases.Comment: 3 pages, 3 postscript figures, submitted to the proceedings of the
10th Brazilian Workshop on Semiconductor Physics (BWSP10
Variational study of the nu=1 quantum Hall ferromagnet in the presence of spin-orbit interaction
We investigate the nu=1 quantum Hall ferromagnet in the presence of
spin-orbit coupling of the Rashba or Dresselhaus type by means of
Hartree-Fock-typed variational states. In the presence of Rashba (Dresselhaus)
spin-orbit coupling the fully spin-polarized quantum Hall state is always
unstable resulting in a reduction of the spin polarization if the product of
the particle charge and the effective -factor is positive (negative). In
all other cases an alternative variational state with O(2) symmetry and finite
in-plane spin components is lower in energy than the fully spin-polarized state
for large enough spin-orbit interaction. The phase diagram resulting from these
considerations differs qualitatively from earlier studies.Comment: 9 pages, 3 figures included, version to appear in Phys. Rev.
Probing entanglement via Rashba-induced shot noise oscillations
We have recently calculated shot noise for entangled and spin-polarized
electrons in novel beam-splitter geometries with a local Rashba s-o interaction
in the incoming leads. This interaction allows for a gate-controlled rotation
of the incoming electron spins. Here we present an alternate simpler route to
the shot noise calculation in the above work and focus on only electron pairs.
Shot noise for these shows continuous bunching and antibunching behaviors. In
addition, entangled and unentangled triplets yield distinctive shot noise
oscillations. Besides allowing for a direct way to identify triplet and singlet
states, these oscillations can be used to extract s-o coupling constants
through noise measurements. Incoming leads with spin-orbit interband mixing
give rise an additional modulation of the current noise. This extra rotation
allows the design of a spin transistor with enhanced spin control.Comment: 7 pages, 3 figures; to appear in the special issue of the Journal of
Superconductivity in honor of E. I. Rashb
Energy spectra for quantum wires and 2DEGs in magnetic fields with Rashba and Dresselhaus spin-orbit interactions
We introduce an analytical approximation scheme to diagonalize parabolically
confined two dimensional electron systems with both the Rashba and Dresselhaus
spin-orbit interactions. The starting point of our perturbative expansion is a
zeroth-order Hamiltonian for an electron confined in a quantum wire with an
effective spin-orbit induced magnetic field along the wire, obtained by
properly rotating the usual spin-orbit Hamiltonian. We find that the
spin-orbit-related transverse coupling terms can be recast into two parts W and
V, which couple crossing and non-crossing adjacent transverse modes,
respectively. Interestingly, the zeroth-order Hamiltonian together with W can
be solved exactly, as it maps onto the Jaynes-Cummings model of quantum optics.
We treat the V coupling by performing a Schrieffer-Wolff transformation. This
allows us to obtain an effective Hamiltonian to third order in the coupling
strength k_Rl of V, which can be straightforwardly diagonalized via an
additional unitary transformation. We also apply our approach to other types of
effective parabolic confinement, e.g., 2D electrons in a perpendicular magnetic
field. To demonstrate the usefulness of our approximate eigensolutions, we
obtain analytical expressions for the n^th Landau-level g_n-factors in the
presence of both Rashba and Dresselhaus couplings. For small values of the bulk
g-factors, we find that spin-orbit effects cancel out entirely for particular
values of the spin-orbit couplings. By solving simple transcendental equations
we also obtain the band minima of a Rashba-coupled quantum wire as a function
of an external magnetic field. These can be used to describe Shubnikov-de Haas
oscillations. This procedure makes it easier to extract the strength of the
spin-orbit interaction in these systems via proper fitting of the data.Comment: 13 pages, 11 figure
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