Unified theory of spin dynamics in a two-dimensional electron gas with arbitrary spin-orbit coupling strength at finite temperature

Abstract

We study the spin dynamics in the presence of impurity and electron-electron (e-e) scattering in a III-V semiconductor quantum well with arbitrary spin-orbit coupling (SOC) strength and symmetry at finite temperature. We derive the coupled spin-charge dynamic equations in the presence of inelastic scattering and provide a new formalism that describes the spin relaxation and dynamics in both the weak and the strong SOC regime in a unified way. In the weak SOC regime, as expected, our theory reproduces all previous zero-temperature results, most of which have focused on impurityscattering induced spin-charge dynamics. In the regime where the strength of the Rashba and linear Dresselhaus SOC match, known as the SU(2) symmetry point, experiments have observed the spinhelix mode with a large spin-lifetime whose unexplained non-monotonic temperature dependence peaks at around 75 K. As a key test of our theory, we are able to naturally explain quantitatively this non-monotonic dependence and show that it arises as a competition between the DyakonovPerel mechanism, suppressed at the SU(2) point, and the Elliott-Yafet mechanism. In the strong SOC regime, we show that our theory directly reproduces the only previous known analytical result at the SU(2) symmetry point in the ballistic regime. It also explains, as we have shown previously, the rise of damped oscillating dynamics when the electron scattering time is larger than half of the spin precession time due to the SOC. Hence, we provide a unified theory of the spin-dynamics in two dimensional electron gases in the full phase diagram experimentally accessible.

Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

“…Therefore, we obtain coupled spin and charge transport equations for SSs of a TI as well as a Rashba 2DEG. For ease of analysis, we begin with the Rashba 2DEG, which is then modified for the TI SSs.Within the parabolic band approximation, the Hamiltonian for the Rashba 2DEG (setting = 1) is [22,27]:Here m is the effective mass, k is the in-plane momentum, σ 0 is the identity matrix, σ = (σ xx + σ yŷ + σ zẑ ) where σ's are the Pauli spin matrices (we have used boldface for matrices in the spin space) and λ is the strength of spin splitting. The spin-charge dynamic equation obtained from quantum kinetic theory can be written in terms of density matrix ρ = ρ 0 σ 0 + ρ · σ (where ρ = ρ xx + ρ yŷ + ρ zẑ ) as ρ r = D rs ρ s (r, s = 0, x, y, z), where D is the diffusion matrix [22,23].…”

“…Previously, the voltage drop measured between a FM and a nonmagnetic (NM) contact placed on the surface of a TI was theoretically calculated either using non-equilibrium Green's function [20] or by solving the transport equations derived from Kubo formalism [21]. Here, we provide a different approach for the derivation of the coupled spin-charge transport differential equation based on quantum kinetic theory [22,23] in the diffusive limit. The experimentally measured spin signal matches well with the theory providing evidence for the spin polarized SS in our TI Bi 2 Te 3 thin film.…”

“…The spin-charge dynamic equation obtained from quantum kinetic theory can be written in terms of density matrix ρ = ρ 0 σ 0 + ρ · σ (where ρ = ρ xx + ρ yŷ + ρ zẑ ) as ρ r = D rs ρ s (r, s = 0, x, y, z), where D is the diffusion matrix [22,23]. The charge and spin densities are given by n = ρ 0 and s = ρ/2, respectively.…”

Room-temperature spin thermoelectrics in metallic films

“…(22) and (24), the charge distribution enters the spin sector, from which we determine f y and hence the spin polarization linear in E x and ∇ x T according to Eq. (25). In the last step, integrating the y spin component of Eq.…”

“…Moreover, we wish to identify the possible connections between the four phenomena. It is known, for example, that in a 2DEG at low T , the spin Hall and Edelstein effects may be related [22][23][24][25], and that such a relation can be extended to thin (quasi-2D) films as well [26]. Whether a connection exists, possibly in a modified form, also at high T or in 3D is an open question.…”