Spin phase protection in interference of electron spin waves in lightly hydrogenated graphene

Abstract

Electron spin transport in graphene is extremely sensitive to foreign atoms and ripples of the SiO₂ substrate. Indeed, the observed spin diffusion- and relaxation-length (time) were smaller than theoretically expected owing to this, although a large spin diffusion length has been recently realized in graphene synthesized on a SiC substrate. It is, thus, crucial to enhance the spin phase coherence and spin diffusion (relaxation) length of a graphene/SiO₂ substrate particularly for future graphene spintronics. One of the approaches to realize this is the investigation of the spin phase in the phase interference phenomena of electron spin waves (such as weak localization (WL)) and its correlation with the spin–orbit-interaction (SOI). However, their coexistence in graphene is difficult to be realized experimentally. Here, we have realized the extremely light hydrogenation of a graphene surface (≪0.1%) on SiO₂ by precisely controlling the amount of electron beam (EB) irradiation to a specific EB resist including hydrogen atoms, treated on graphene. It allows the coexistence of WL and the SOI. We find spin phase protection (suppression of dephasing) of the electron-spin-waves in the WL on temperature and external magnetic-field dependence in the graphenes with hydrogenation volumes (N_H) as small as 0.06%. As an origin, correlation of the WL with a Rashba-type SOI, which can be introduced by out-of-plane symmetry breaking due to the formation of sp³ bonds derived from the small N_H, is discussed. The present finding in lightly hydrogenated graphene must be beneficial for graphene spintronics, which requests a long spin diffusion- and coherence-length. It will realize a possible 2D-topological insulating state in graphene.