Universal Rashba spin precession of two-dimensional electrons and holes

Abstract

Abstract. -We study spin precession due to Rashba spin splitting of electrons and holes in semiconductor quantum wells. Based on a simple analytical expression that we derive for the current modulation in a broad class of experimental situations of ferromagnet/nonmagnetic semiconductor/ferromagnet hybrid structures, we conclude that the Datta-Das spin transistor (i) is feasible with holes and (ii) its functionality is not affected by integration over injection angles. The current modulation shows a universal oscillation period, irrespective of the different forms of the Rashba Hamiltonian for electrons and holes. The analytic formulas approximate extremely well exact numerical calculations of a more elaborate Kohn-Luttinger model.Transport effects based on coherent manipulation of the spin degree of freedom in lowdimensional semiconductors are currently attracting a lot of attention [1]. These studies, enabled by recent progress in nanofabrication technology to create high-quality samples, are motivated by both their interesting fundamental physics and their potential for future device applications [2]. A lot of progress in the field has been stimulated by the exploitation of spin precession due to Rashba spin-orbit (SO) coupling in 2D systems both for electrons [3][4][5] and for holes [6]. A prominent example is the spin-controlled field-effect transistor (spin FET) introduced by Datta and Das [7], followed by more recent proposals for novel devices utilizing Rashba SO coupling [8]. Both in the original [7] and most subsequent [9][10][11][12][13][14] works, a quasionedimensional (1D) confinement was considered essential for proper spin-FET action. Spin precession in truly 2D electron systems was studied numerically in a number of works [15,16]. On the other hand, ever-present spin relaxation will reduce the spin polarization of currents, preventing the realization of gate-controlled modulation. Such processes arise, e.g., from magnetic impurities but most importantly from elastic impurity scattering that randomizes the direction of the effective Rashba field. Stronger spin-orbit coupling and band mixing phenomena imply a shorter spin relaxation time for the holes respect to the electrons, that can be compensated by shorter precession length. A nice proposal, which exploits tunability of Rashba SO coupling, to overcome the detrimental effects due to scattering processes is presented in the last paper of Ref. [8].c EDP Sciences

Conductance oscillations of a spin-orbit stripe with polarized contacts

“…In this section we discuss the dependence on α 0 , considering first fully polarized contacts (E < 2∆ 0 ) and, subsequently, partial polarization at the end of the section. The fully polarized results agree overall with other theoretical analysis [22][23][24] and, qualitatively, with the experiments of Koo et al. 8 Quite surprisingly, however, the oscillatory character of the conductance is rapidly washed out if partial polarization is considered in our model by increasing the energy above the Zeeman threshold E > 2∆ 0 .…”

“…Similar damped oscillations were obtained in Refs. [22][23][24]. Notice also that this damping is due to the Rashba mixing since it is absent in the open symbols.…”

“…[17][18][19] while the 2D system, without confinement in the transverse direction, has been also addressed in Refs. [20][21][22][23][24][25]. In most cases sharp transitions between the contacts and the channel are assumed and matching of the wave functions at the interfaces is the required condition.…”

Thermoelectric effects in graphene with local spin-orbit interaction

“…In semiconductor quantum wires with parabolic confinement, the presence of localized Rashba interaction has been predicted to yield Fano antiresonances [20][21][22][23][24][25], to help the detection of entangled electrons [26][27][28], and to assist electron-spin resonance manipulation [29][30][31]. The effect of nonhomogeneous Rashba couplings has also been considered in the transport characteristics of two-dimensional systems [32][33][34][35][36]. A natural question is thus to what extent these results are modified in graphene monolayers.…”

Interference of heavy holes in an Aharonov-Bohm ring

“…These studies are relevant because of the strong spin-orbit coupling of heavy holes confined to the ring [15], and long coherence length (∼ 3 µm in carbondoped GaAs), making the interference effects in transport observable. The material parameters of holes allow for spintronic applications [17]. In coherent spin-orbit coupled systems, the transport shows an intriguing interplay of Aharonov-Bohm and Aharonov-Casher effects [18].…”