Comparison between charge and spin transport in few layer graphene

TL;DR

This study compares charge and spin transport in few-layer graphene, revealing how layer number and gating influence transport properties and spin relaxation, with measurements showing extended spin signals and relaxation times.

Contribution

It provides a systematic analysis of charge and spin transport in FLG, including the effects of layer number and gating, and compares results with single-layer graphene.

Findings

Spin signals observed up to 10 μm distance

Spin relaxation times up to 500 ps, four times higher than in SLG

Charge and spin diffusion coefficients show similar weak dependence on layers

Abstract

Transport measurements on few layer graphene (FLG) are important as they interpolate between the properties of single layer graphene (SLG) as a true 2-dimensional material and the 3-dimensional bulk properties of graphite. In this article we present 4-probe local charge transport and non-local spin valve and spin precession measurements on lateral spin field-effect transistors (FET) on FLG. We study systematically the charge and spin transport properties depending on the number of layers and the electrical back gating of the device. We explain the charge transport measurements by taking the screening of scattering potentials into account and use the results to understand the spin data. The measured samples are between 3 and 20 layers thick and we include in our analysis our earlier results of the measurements on SLG for comparison. In our room temperature spin transport measurements we manage to observe spin signals over distances up to 10 u m and measure spin-relaxation times up to tau_s ~500 ps, about 4 times higher than in SLG. We calculate the density of states (DOS) of FLG using a zone-folding scheme to determine the charge diffusion coefficient D_C from the square resistance R_S. The resulting D_C and the spin diffusion coefficient D_S show similar values and depend only weakly on the number of layers and gate induced charge carriers. We discuss the implications of this on the identification of the spin-relaxation mechanism.