Spin-orbit interaction and spin relaxation in a two-dimensional electron gas

Abstract

Using time-resolved Faraday rotation, the drift-induced spin-orbit field of a two-dimensional electron gas in an InGaAs quantum well is measured. Including measurements of the electron mobility, the Dresselhaus and Rashba coefficients are determined as a function of temperature between 10 and 80 K. By comparing the relative size of these terms with a measured in-plane anisotropy of the spin-dephasing rate, the D'yakonv-Perel' contribution to spin dephasing is estimated. The measured dephasing rate is significantly larger than this, which can only partially be explained by an inhomogeneous g factor.The possibility to manipulate spins in semiconductors is a requirement for future spin-based information processing.1 Using the spin-orbit (SO) interaction 2,3 is a promising way to precisely control spin polarization because of its simple principle based on external gate electrodes.4,5 Manipulation of spins using the SO interaction has been shown in various semiconductor systems, such as bulk semiconductors 6 , two-dimensional electron gases 7 (2DEGs), and even quantum dots containing only one single electron.8 On the other hand, the SO interaction is a source for spin dephasing. In 2DEGs, the SO interaction induces a linear k-dependent splitting.9 This splitting gives rise to an effective magnetic field, leading to dephasing of the polarized electron spins.10 This effect is known as the D'yakonv-Perel' (DP) mechanism, and its control through manipulation of the SO interaction has been proposed 11 as an alternative to the ballistic spin transistor.4 A careful engineering of the SO interaction is therefore crucial for using it to manipulate the spin.In a 2DEG at intermediate temperatures, it is often assumed that the spin decay is governed by the DP mechanism.12,13 Based on this assumption, information on the SO interaction in semiconductor quantum wells (QWs) was obtained from measurements of the spin-dephasing rate.14,15,16 An independent measurement of the relative size of the SO interaction in (110)-grown QWs using the photogalvanic effect has been described in Ref. 17 and compared to the spin decay time. In this paper, we report on quantitative and independent measurements of the SO interaction and the spin-dephasing rate in an InGaAs QW, utilizing time-resolved Faraday rotation. In a further development of the method described in Ref. 7, a well-defined current is applied in the 2DEG using Ohmic contacts and a mesa structure (in Ref. 7, the electron drift was induced by an ac voltage applied to Schottky contacts in an unstructured 2DEG). The drifting electrons see an effective SO magnetic field, in the following referred to as drift SO field. The sizes of its two contributions, the Rashba 3 and the Dresselhaus 2 fields, are determined as a function of temperature T from the measured influence of the in-plane electron drift velocity on the spin precession. Comparing our results with mea- sured spin-dephasing rates and their in-plane anisotropy, we find that DP is not the only mechanism for spin decay in our samples...

Spin dynamics in semiconductors

“…48 The spin relaxation anisotropy in (001) quantum wells was first observed by Averkiev et al [198] via the Hanle measurements, and then by several groups via time-resolved measurements [66,199,598,599]. Among these works, the spin relaxation anisotropy was demonstrated to be controlled/affected by density [598], magnetic field [199], gate-voltage (see Fig.…”

“…The interference of the two spin-orbit couplings leads to anisotropic spin splitting, which hence results in anisotropic spin precession [64][65][66][67], spin relaxation [194][195][196][197][198][199], spin diffusion [29,[32][33][34]37] and spin photocurrent [200][201][202]. Conversely, the ratio of β D /α R can be inferred from the anisotropy of spin precession [64,203], spin relaxation [198,199], spin diffusion [29,33] and spin photocurrent [200,201].…”

“…Among these works, the spin relaxation anisotropy was demonstrated to be controlled/affected by density [598], magnetic field [199], gate-voltage (see Fig. 7) [599,600] and temperature [66,598]. The symmetry of the spin-orbit coupling in other two-dimensional structures with different growth directions also has a marked effect on spin relaxation.…”

“…The spin relaxation rate due to the Bir-Aronov-Pikus mechanism is usually calculated via Eq. (66), which actually implies the elastic scattering approximation [118,390,390,391]. Recently Zhou and Wu [109] reinvestigated the Bir-Aronov-Pikus spin relaxation without such an approximation from the fully microscopic kinetic spin Bloch equation approach [44,334,350].…”

“…For example, spin-orbit couplings enable coherent manipulation of spin by an electric field [53,[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76]. As the electric field is more easily accessible and controllable in genuine electronic devices at the nanoscale, the electrical manipulation of spins is important for semiconductor spintronics.…”