Substrate Effects on Spin Relaxation in Two-Dimensional Dirac Materials with Strong Spin-Orbit Coupling

TL;DR

This study investigates how different substrates influence spin relaxation in 2D Dirac materials with strong spin-orbit coupling, revealing substrate-induced changes in spin dynamics and proposing a new parameter to control spin relaxation.

Contribution

The paper introduces a first-principles simulation approach to analyze substrate effects on spin relaxation in germanene and proposes the spin-flip angle as a new control parameter.

Findings

Substrate effects on spin lifetime can differ by two orders of magnitude.

Spin relaxation is linked to substrate-induced SOC-field anisotropy modifications.

The spin-flip angle correlates with the spin relaxation rate.

Abstract

Understanding substrate effects on spin dynamics and relaxation in two-dimensional (2D) materials is of key importance for spintronics and quantum information applications. However, the key factors that determine the substrate effect on spin relaxation, in particular for materials with strong spin-orbit coupling, have not been well understood. Here we performed first-principles real-time density-matrix dynamics simulations with spin-orbit coupling (SOC) and quantum descriptions of electron-phonon and electron-impurity scattering for the spin lifetimes of supported/free-standing germanene, a prototypical strong SOC 2D Dirac material. We show that the effects of different substrates on spin lifetime can surprisingly differ by two orders of magnitude. We find that substrate effects on $\tau_s$ are closely related to substrate-induced modifications of the SOC-field anisotropy, which changes the spin-flip scattering matrix elements. We propose a new electronic quantity, named spin-flip angle $\theta^{\uparrow\downarrow}$, to characterize spin relaxation caused by intervalley spin-flip scattering. We find that the spin relaxation rate is approximately proportional to the averaged value of $\mathrm{sin}^{2}\left(\theta^{\uparrow\downarrow}/2\right)$, which can be used as a guiding parameter of controlling spin relaxation.