Electron spin relaxation in rippled graphene with low mobilities

TL;DR

This study explores how ripples and low mobility in graphene influence spin relaxation, revealing anisotropic relaxation times affected by temperature and magnetic fields, with implications for spintronic applications.

Contribution

It uncovers a temperature-dependent spin relaxation channel in rippled graphene caused by curvature-induced spin-orbit coupling and intervalley phonon scattering, which was not previously characterized.

Findings

Spin relaxation time for spins perpendicular to the effective magnetic field shows a minimum around room temperature.

Spin relaxation along the effective magnetic field remains nearly constant at microseconds over temperature.

In-plane spin relaxation is highly anisotropic but becomes isotropic under a small perpendicular magnetic field.

Abstract

We investigate spin relaxation in rippled graphene where curvature induces a Zeeman-like spin-orbit coupling with opposite effective magnetic fields along the graphene plane in ${\bf K}$ and ${\bf K}^\prime$ valleys. The joint effect of this Zeeman-like spin-orbit coupling and the intervalley electron-optical phonon scattering opens a spin relaxation channel, which manifests itself in low-mobility samples with the electron mean free path being smaller than the ripple size. Due to this spin relaxation channel, with the increase of temperature, the relaxation time for spins perpendicular to the effective magnetic field first decreases and then increases, with a minimum of several hundred picoseconds around room temperature. However, the spin relaxation along the effective magnetic field is determined by the curvature-induced Rashba-type spin-orbit coupling, leading to a temperature-insensitive spin relaxation time of the order of microseconds. Therefore, the in-plane spin relaxation in low-mobility rippled graphene is anisotropic. Nevertheless, in the presence of a small perpendicular magnetic field, as usually applied in the Hanle spin precession measurement, the anisotropy of spin relaxation is strongly suppressed.