Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization

Abstract

Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization Kaverzin, A. A.; van Wees, B. J. A number of practical and fundamental applications of graphene requires modification of some of its properties. In this paper we study the effect of polymerization of a hydrogen silsesquioxane film on top of monolayer graphene with the intent to increase the strength of the spin-orbit interaction. The measured nonlocal resistances R NL were found to be up to 700 , significantly exceeding the expected contribution from conventional Ohmic currents. The R NL dependence on the channel length resembles exponential decay with a characteristic length of λ 500 nm that is close to the spin-relaxation length in graphene reported elsewhere. The sensitivity of the measured effect to the electron-beam exposure was shown to decrease with an increased level of the surface contamination. However, no modulation of the effect is observed when an in-plane magnetic field is applied. This implies that a spin Hall model fails to explain the observed phenomenon and an alternative interpretation is required.

Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene

“…This is especially true when the impurity-induced Rashba is large, as it may be the case of hydrogenated graphene 18,24 ; such an analysis will be presented elsewhere 47 . The present theory may also have important implications for understanding recent spin pumping experiments in CVD graphene involving the inverse of CISP 26 and the inverse of current-induced spin current 25,27 .…”

“…Since our theory assumes that the SOC disorder stems from localized impurities (e.g. adatoms 17,18,24 ), the EY relaxation is caused by spin-flip scattering events. This form of EY spin relaxation is akin to the one considered by Lifshits and Dyakonov in Ref.…”

“…The new ASP scattering contribution to the spin current calls for a need to revise the existing SHE theory 46 which has been customarily employed to fit the nonlocal resistance data in Hall bar spin-transport experiments 17,18,23,24 . This is especially true when the impurity-induced Rashba is large, as it may be the case of hydrogenated graphene 18,24 ; such an analysis will be presented elsewhere 47 .…”

“…So far, however, simulations based on the Kubo formalism 34,35 have been limited to impurity densities of 10%, significantly higher than in typical experiments 17,18,24 ( 1%). It is uncertain whether these numerical methods can be extrapolated to the dilute impurity regime, due to the different, density dependent mechanisms involved in the SHE 20,36,37 .…”

“…This paper presents an analytical theory of spincoherent transport for extrinsic SOC in graphene, based on the linearized Quantum Boltzmann Equation (QBE). It incorporates coherent spin dynamics into the transport equations by treating both types of extrinsic SOC on equal footing, and is directly applicable to the experimentally-relevant limit of strongly-scattering but dilute impurities 17,18,24 . From the theory, we uncover a novel extrinsic SOC scattering process, "anisotropic spin precession" (ASP) scattering, which involves a combination of skew and spin-flip scattering.…”