Oscillatory D'yakonov-Perel' spin dynamics in two dimensional electron gases

TL;DR

This study investigates spin dynamics in high-mobility GaAs/AlGaAs quantum wells at very low temperatures, revealing oscillatory behavior consistent with D'yakonov-Perel' theory and providing insights into spin-orbit interactions.

Contribution

It demonstrates the oscillatory spin dynamics in 2DEGs and uses Monte Carlo simulations to extract key spin-orbit parameters, advancing understanding of spin behavior in quantum wells.

Findings

Spin dynamics are oscillatory rather than exponential at low temperatures.

Monte Carlo simulations accurately extract spin precession frequency and scattering times.

Spin-orbit interaction strength varies with quantum well confinement energy.

Abstract

Optical pump-probe measurements of spin-dynamics at temperatures down to 1.5K are described for a series of (001)-oriented GaAs/AlGaAs quantum well samples containing high mobility two-dimensional electron gases (2DEGs). For well widths ranging from 5 nm to 20 nm and 2DEG sheet densities from 1.75x1011cm-2 to 3.5x1011cm-2 the evolution of a small injected spin population is found to be a damped oscillation rather than exponential relaxation, consistent with the quasi-collision-free regime of D'yakonov-Perel spin dynamics. A Monte Carlo simulation method is used to extract the spin-orbit-induced electron spin precession frequency |W(kF)| and electron momentum scattering time tp* at the Fermi wavevector. The spin decay time passes through a minimum at a temperature corresponding to the transition from collision-free to collision-dominated regimes and tp* is found to be close to the ensemble momentum scattering time tp obtained from Hall measurements of electron mobility. The values of |W(kF)| give the Dresselhaus (BIA) coefficient of spin-orbit interaction as a function of electron confinement energy in the quantum show, qualitatively, the behaviour expected from k.p theory.