Nonlocal spin dynamics in the crossover from diffusive to ballistic transport

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. ; M. V. acknowledges support from "La Caixa" Foundation. S. R. P. acknowledges funding from the Irish Research Council under the Laureate awards programme. X. W. acknowledges the ANR GRANSPORT funding. All authors were supported by the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 785219 (Graphene Flagship). ICN2 is funded by the CERCA Programme/Generalitat de Catalunya, and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). ; Peer reviewed