Current-Controlled Spin Precession of Quasistationary Electrons in a Cubic Spin-Orbit Field

Abstract

Space-and time-resolved measurements of spin drift and diffusion are performed on a GaAs-hosted two-dimensional electron gas. For spins where forward drift is compensated by backward diffusion, we find a precession frequency in absence of an external magnetic field. The frequency depends linearly on the drift velocity and is explained by the cubic Dresselhaus spin-orbit interaction, for which drift leads to a spin precession angle twice that of spins that diffuse the same distance.Drift and diffusion of charge carriers in semiconductor nanostructures are the foundation of information technology. The spin of the electron is being investigated as an additional or complementary degree of freedom that can enhance the functionality of electronic devices and circuits [1][2][3]. In the presence of spin-orbit interaction (SOI), the spins of moving electrons precess about effective magnetic fields that depend on the electron momentum vector, k [4]. In a two-dimensional electron gas (2DEG), this precession has been proposed as a gatetunable switching mechanism [5,6]. Spin diffusion and spin drift have been studied using optical [7][8][9][10][11] and electrical techniques [12,13]. A local spin polarization expands diffusively into a spin mode with a spatial polarization pattern that is characteristic of the strength and symmetry of the SOI [14]. An additional drift induced by an electric field does not modify the spatial precession period in the case of linear SOI [15][16][17][18]. This is because spins that travel a certain distance and direction precess on average by the same angle, irrespective of how the travel is distributed between diffusion and drift. Therefore, no spin precession occurs for quasi-stationary electrons, i.e. for electrons where drift is compensated by diffusion.In this letter, we experimentally observe such unexpected drift-induced spin precession of stationary electron spins in the absence of an external magnetic field. Using an optical pump-probe technique, we investigate the spatiotemporal dynamics of locally excited spin polarization in an n-doped GaAs quantum well. Spin polarization probed at a fixed position is found to precess with a finite frequency, ω. This is identified as a consequence of cubic SOI, which affects spin drift and spin diffusion differently. A simple model predicts that drifting spins precess twice as much as spins that diffuse the same distance. This difference leads to a dependence ω ∝ β 3 v dr , where β 3 is the cubic SOI coefficient and v dr the drift velocity. We demonstrate quantitative agreement between model and experiment, and extract a β 3 in agreement with literature values. Monte-Carlo simulations confirm the validity of the model and pinpoint deviations that occur when the drift-induced SOI field is small compared arXiv:1602.05095v3 [cond-mat.mes-hall]

Spin drift and diffusion in one- and two-subband helical systems

“…We show that a finite in-plane drift field (e.g., along y [110]) leads to distinct precession patterns and relaxation rates for the PSH regimes α = ±(β 1 − β 3 ), which we label as PSH + and PSH − , respectively. Our PSH + solution matches previous discussions in the literature [3,4,18,19,26]. More interestingly, for the PSH − regime, the drift velocity shifts the maximum spin lifetime away from the precise PSH tuning.…”

“…The theoretical analysis of the drift field on the diffuse spin dynamics were first presented in Refs. 3 and 5 for a single-subband system, and recently observed experimentally [26]. In this section we explore and extend these results using the RW model.…”

“…These regimes are different because we keep the drift velocity fixed alongŷ. Equivalently, for a fixed set of SOC coefficients one could alternate between the PSH ± regimes switching the drift velocity direction [26] between x andŷ. These and the following images are saturated for better visualization of the magnetization patterns.…”

“…The effects of a drift field [3,5] on the dynamics of the PSH states were recently observed [26], allowing a direct measurement of the cubic Dresselhaus coupling β 3 . More recently, for two-subband systems, it was shown [35] that a crossed-PSH regime (Rashba SOC with opposite sign in each subband) leads to nontrivial spin patterns, which may lead to a topological Hall effect [36].…”

Deterministic transfer of spin polarization in wire-like lateral structures via the persistent spin helix

“…15 Very recently, investigations in biased structures under charge transport were reported. 16,17 In this work, we used spatially-and time-resolved Kerr rotation microscopy to show that spin polarization can be deterministically transferred to specific lateral positions via the PSH. We started by experimentally verifying the PSH in the as-grown sample, a GaAs-AlGaAs single quantum well, via spatially-resolved Kerr microscopy, followed by the investigation of narrow channels with lateral widths down to 3 lm.…”