Pseudo spin torque induced by strain field of Dirac fermions in graphene

TL;DR

This paper clarifies the nature of pseudo spin in graphene, showing its directional dependence and revealing its analogy to gravitomagnetic effects under strain, thus uncovering new physical properties of graphene.

Contribution

It demonstrates that pseudo spin in graphene is not entirely a real angular momentum and establishes an analogy between pseudo spin torque and gravitomagnetic phenomena.

Findings

Pseudo spin perpendicular to graphene is real angular momentum.

Pseudo spin parallel to graphene is not real angular momentum.

Strain-induced pseudo spin torque mimics gravitomagnetic spin torque.

Abstract

In contrast to recent description [Phys. Rev. Lett. 106 (2011)116803], we show that pseudo spin in graphene is not completely a real angular momentum. The pseudo spin only in the direction perpendicular to graphene sheet is real angular momentum, while the pseudo spin parallel to graphene plane is still not real angular momentum. Interestingly, it is also shown that the Newtonian-like force and pseudo spin torque of massive Dirac electrons in graphene under strain field mimic gravitomagnetic force and gravitomagnetic spin torque, respectively. This is due to the equivalence of pseudo spin and velocity operators of 2+1 dimensional massive electrons in graphene, different from that in real 3+1 dimensional Dirac fields. This work reveals new physical property of graphene as a pseudo gravitomagnetic material.