Spin Relaxation and Diffusion in Monolayer 1T'-WTe$_2$ from First-Principles

TL;DR

This study uses a novel first-principles approach to analyze spin relaxation in monolayer 1T'-WTe$_2$, revealing complex mechanisms and promising spintronic properties at room temperature.

Contribution

It introduces an ab initio density-matrix dynamics method to investigate spin relaxation in topological materials, uncovering new relaxation behaviors beyond traditional models.

Findings

Spin lifetime shows large anisotropy along certain directions.

Opposite trends in spin and carrier relaxation under electric field.

Predicted spin lifetime ~1 ps and diffusion length ~30 nm at room temperature.

Abstract

Understanding spin relaxation in topological systems such as quantum spin-hall (QSH) insulator is critical for realizing coherent transport at high temperature. WTe$_{2}$, known as a QSH insulator with a high transition temperature of 100K, is an important test-bed of unveiling spin relaxation mechanism in topological materials. In this work, we employ our recently-developed \emph{ab initio} density-matrix dynamics approach to investigate spin relaxation mechanism, and calculate spin lifetime and diffusion length of monolayer 1T'-WTe$_{2}$, at finite temperature under an external electric field. We found the spin lifetime of electrons have the largest anisotropy when measuring along the canted-spin-texture direction. Moreover, we found an opposite trend between spin and carrier relaxation against applied electric field. Most importantly, the relaxation mechanism under intermediate electric field around 1V/nm can not be explained by either Eillot-Yafet or Dyakonov-Perel models, which highlights the generality of our \emph{ab initio} density-matrix framework. We then proposed analytical models to explain its mechanism and compare well with \emph{ab initio} results at small and large electric field. We predict that spin lifetime and spin diffusion length of bulk-state electrons are $\sim$1 ps and $\sim$30 nm at room temperature respectively, suggesting its promise for spintronic applications.