Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport

TL;DR

This study uses quantum simulations to analyze spin transport in ultraclean graphene devices, revealing limitations of traditional diffusion theory in ballistic and long spin diffusion regimes, and proposing an extended theoretical framework.

Contribution

It introduces an extended theoretical model to accurately describe spin transport in graphene across diffusive, ballistic, and long diffusion length regimes.

Findings

Conventional spin diffusion theory fails in ballistic and long diffusion regimes.

Quantum simulations reveal the crossover behaviors in spin transport.

An extended framework accurately describes long spin diffusion lengths.

Abstract

Improved fabrication techniques have enabled the possibility of ballistic transport and unprecedented spin manipulation in ultraclean graphene devices. Spin transport in graphene is typically probed in a nonlocal spin valve and is analyzed using spin diffusion theory, but this theory is not necessarily applicable when charge transport becomes ballistic or when the spin diffusion length is exceptionally long. Here, we study these regimes by performing quantum simulations of graphene nonlocal spin valves. We find that conventional spin diffusion theory fails to capture the crossover to the ballistic regime as well as the limit of long spin diffusion length. We show that the latter can be described by an extension of the current theoretical framework. Finally, by covering the whole range of spin dynamics, our study opens a new perspective to predict and scrutinize spin transport in graphene and other two-dimensional material-based ultraclean devices.