Browsing by Subject "Rashba spin-orbit coupling"

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Open Access
Landau quantization of two-dimensional heavy holes, energy spectrum of magnetoexcitons and Auger-recombination lines
(2013) Podlesny I.V.; Moskalenko, S.A.; Hakioǧlu, T.; Kiselyov, A.A.; Gherciu L.
The Landau quantization of the two-dimensional (2D) heavy holes, its influence on the energy spectrum of 2D magnetoexcitons, as well as their optical orientation are studied. The Hamiltonian of the heavy holes is written in two-band model taking into account the Rashba spin-orbit coupling (RSOC) with two spin projections, but with nonparabolic dispersion law and third-order chirality terms. The most Landau levels, except three with m=0,1,2, are characterized by two quantum numbers m-3 and m for m≥3 for two spin projections correspondingly. The difference between them is determined by the third-order chirality. Four lowest Landau levels (LLLs) for heavy holes were combined with two LLLs for conduction electron, which were taken the same as they were deduced by Rashba in his theory of spin-orbit coupling (SOC) based on the initial parabolic dispersion law and first-order chirality terms. As a result of these combinations eight 2D magnetoexciton states were formed. Their energy spectrum and the selection rules for the quantum transitions from the ground state of the crystal to exciton states were determined. On this base such optical orientation effects as spin polarization and magnetoexciton alignment are discussed. The continuous transformation of the shake-up (SU) into the shake-down (SD) recombination lines is explained on the base of nonmonotonous dependence of the heavy hole Landau quantization levels as a function of applied magnetic field. © 2013 Elsevier B.V. All rights reserved.
Open Access
Mesoscopic Fano effect in a spin splitter with a side-coupled quantum dot
(Elsevier B.V., 2012) Moldoveanu, V.; Tolea, M.; Tanatar, Bilal
We investigate the interplay between the spin interference and the Fano effect in a three-lead mesoscopic ring with a side-coupled quantum dot (QD). A uniform Rashba spin-orbit coupling and a perpendicular magnetic field are tuned such that the ring operates as a spin splitter in the absence of the QD: one lead is used to inject unpolarized electrons and the remaining (output) leads collect almost polarized spin currents. By applying a gate potential to the quantum dot a pair of spin-split levels sweeps the bias window and leads to Fano interference. The steady-state spin and charge currents in the leads are calculated for a finite bias applied across the ring via the non-equilibrium Green's function formalism. When the QD levels participate to transport we find that the spin currents exhibit peaks and dips whereas the charge currents present Fano lineshapes. The location of the side-coupled quantum dot and the spin splitting of its levels also affect the interference and the output currents. The opposite response of output currents to the variation of the gate potential allows one to use this system as a single parameter current switch. We also analyze the dependence of the splitter efficiency on the spin splitting on the QD.
Open Access
Optical properties of the two-dimensional magnetoexcitons under the influence of the Rashba spin-orbit coupling
(SPIE, 2011) Hakioglu, Tuğrul; Liberman, M.A.; Moskalenko, S.A.; Podlesny I.V.
The influence of the Rashba spin-orbit coupling on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results of the Landau quantization in different spin projections. In Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of the Landau quantization levels are different. For electron in s-type conduction band they differ by one, as was established earlier by Rashba1, whereas for heavy holes in p-type valence band influenced by the 2D symmetry of the layer they differ by three. There are two lowest spin-splitted Landau levels for electrons as well as two lowest for holes. They give rise to four lowest energy levels of the 2D magnetoexcitons. It is shown that two of them are dipole-active in band-to-band quantum transitions, one is quadrupole-active and the fourth is forbidden. The optical orientation under the influence of the circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections on the direction of the external magnetic field. © 2011 SPIE.
Open Access
Spin filtering in a quantum ring with Rashba coupling
(IEEE, 2010) Tanatar, Bilal; Moldoveanu V.
We study the effect of Rashba spin-orbit coupling on the spin interference in a non-interacting one-dimensional ring connected to two lead theoretically within the non-equilibrium Greens' function formalism. We compute the charge and spin currents and analyze their Aharonov-Bohm oscillations. The geometry of the system is conveniently described by the angle δ between the two leads. We show that for δ=180° (i.e for symmetrically coupled leads) a good tutering of up or down spin orientation is obtained around half-integer multiples of Φ/Φ0. These particular flux values correspond to degeneracy points for clockwise and counter-clockwise propagating state related to the same spin orientation in the local spin frame of the ring. In contrast, for the asymmetric coupling, i.e., δ=135° the filter efficiency is maximum around integer multiples of Φ/Φ0. The numerical results suggest that the spin filtering is obtained when the clockwise or counter-clockwise states interfere destructively. The spin filtering regime is stable against variations of the bias applied on the system. ©2010 IEEE.