Spin diffusion/transport in $n$-type GaAs quantum wells

TL;DR

This paper investigates spin diffusion and transport in n-type GaAs quantum wells at high temperatures, revealing intrinsic oscillations and the effects of scattering, temperature, and external fields through numerical solutions of kinetic spin Bloch equations.

Contribution

It provides a comprehensive numerical analysis of spin dynamics in GaAs quantum wells, explicitly including electron-electron Coulomb scattering and hot-electron effects, which was not thoroughly explored before.

Findings

Spin polarization oscillates along the transport direction without external magnetic field.

Strong scattering causes spins with different momenta to oscillate in phase, leading to equal injection lengths.

Oscillation period is nearly independent of external electric field, matching low-temperature bulk experiments.

Abstract

The spin diffusion/transport in $n$-type (001) GaAs quantum well at high temperatures ($\ge120$ K) is studied by setting up and numerically solving the kinetic spin Bloch equations together with the Poisson equation self-consistently. All the scattering, especially the electron-electron Coulomb scattering, is explicitly included and solved in the theory. This enables us to study the system far away from the equilibrium, such as the hot-electron effect induced by the external electric field parallel to the quantum well. We find that the spin polarization/coherence oscillates along the transport direction even when there is no external magnetic field. We show that when the scattering is strong enough, electron spins with different momentums oscillate in the same phase which leads to equal transversal spin injection length and ensemble transversal injection length. It is also shown that the intrinsic scattering is already strong enough for such a phenomena. The oscillation period is almost independent on the external electric field which is in agreement with the latest experiment in bulk system at very low temperature [Europhys. Lett. {\bf 75}, 597 (2006)]. The spin relaxation/dephasing along the diffusion/transport can be well understood by the inhomogeneous broadening, which is caused by the momentum-dependent diffusion and the spin-orbit coupling, and the scattering. The scattering, temperature, quantum well width and external magnetic/electric field dependence of the spin diffusion is studied in detail.