Graphene magnetoresistance in a parallel magnetic field: Spin polarization effect

TL;DR

This paper presents a theoretical study of how in-plane magnetic fields affect graphene's magnetoresistance, revealing unique spin polarization effects and non-monotonic behavior in extrinsic graphene.

Contribution

The authors develop a novel theory predicting non-monotonic magnetoresistance in graphene due to spin polarization, highlighting residual conductivity of minority spins at zero density.

Findings

Intrinsic graphene shows negative magnetoresistance proportional to B^2.

Extrinsic graphene exhibits positive then negative magnetoresistance with increasing B.

Residual conductivity of minority spins persists even at zero density.

Abstract

We develop a theory for graphene magnetotransport in the presence of carrier spin polarization as induced, for example, by the application of an in-plane magnetic field ($B$) parallel to the 2D graphene layer. We predict a negative magnetoresistance $\sigma \propto B^2$ for intrinsic graphene, but for extrinsic graphene we find a non-monotonic magnetoresistance which is positive at lower magnetic fields (below the full spin-polarization) and negative at very high fields (above the full spin-polarization). The conductivity of the minority spin band $(-)$ electrons does not vanish as the minority carrier density ($n_-$) goes to zero. The residual conductivity of $(-)$ electrons at $n_- = 0$ is unique to graphene. We discuss experimental implications of our theory.