CT invariant quantum spin Hall effect in a ferromagnetic graphene

Abstract

We predict a quantum spin Hall effect (QSHE) in the ferromagnetic graphene under a magnetic field. Unlike the previous QSHE, this QSHE appears in the absence of any spin-orbit interaction, thus, arrived from a different physical origin. The previous QSHE is protected by the time-reversal (T) invariance. This new QSHE is protected by the CT invariance, where C is the charge conjugation operation. Due to this QSHE, the longitudinal resistance exhibits quantum plateaus. The plateau values are at 1/2, 1/6, 3/28, ..., (in the unit of $h/e^2$), depending on the filling factors of the spin-up and spin-down carriers. The spin Hall resistance is also investigated and is found to be robust against the disorder.