Spin current generation by thermal gradient in graphene/h-BN/graphene lateral heterojunctions

Electron transport driven by a temperature gradient in a transport junction constructed by connecting a zigzag hexagonal boron nitride (h-BN) nanoribbon between two graphene nanoribbons (Gr/BN/Gr) is studied by density functional calculations and non-equilibrium Green's function method. When the zigzag-edged graphene nanoribbons are in the ferromagnetic configuration, the BN barrier introduces a spin-dependent scattering and causes an 'X'-type spin-dependent transmission functions around the Fermi level at equilibrium. In a linear response approximation, this gives rise to a Seebeck thermopower with opposite signs for different spins. It drives electrons with different spins to flow in opposite directions under a finite temperature gradient. Calculations show that the charge current is zero while spin current is not, thus pure spin current is generated. These findings suggests the great importance of BN barrier in the generation of thermal spin current using graphene and the idea should be taken into consideration in the design of spintronic devices using two dimensional materials. (paper)