Topological spin Hall and spin Nernst effects in a bilayer graphene

TL;DR

This paper investigates the intrinsic spin Hall and spin Nernst effects in bilayer graphene, analyzing how external voltage influences phase transitions between topological and conventional insulator states.

Contribution

It provides a detailed theoretical analysis of spin transport phenomena in bilayer graphene, including the effects of external voltage on topological phase transitions.

Findings

Transition from topological spin Hall insulator to conventional insulator with increasing voltage

Comparison of conductivities from tight-binding and effective Hamiltonians

Influence of intrinsic spin-orbit interaction on spin transport properties

Abstract

We consider intrinsic contributions to the spin Hall and spin Nernst effects in a bilayer graphene. The relevant electronic spectrum is obtained from the tight binding Hamiltonian, which also includes the intrinsic spin-orbit interaction. The corresponding spin Hall and spin Nernst conductivities are compared with those obtained from effective Hamiltonians appropriate for states in the vicinity of the Fermi level of a neutral bilayer graphene. Both conductivities are determined within the linear response theory and Green function formalism. The influence of an external voltage between the two atomic sheets is also included. We found transition from the topological spin Hall insulator phase at low voltages to conventional insulator phase at larger voltages.