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

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 regimes 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 impurity-scattering 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 spin-helix mode with a large spin-lifetime whose unexplained nonmonotonic temperature dependence peaks at around 75 K. As a key test of our theory, we are able to naturally explain quantitatively this nonmonotonic dependence and show that it arises as a competition between the Dyakonov-Perel 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.