Nonreciprocal spin transport in twisted bilayer zigzag graphene nanoribbons

Zigzag graphene nanoribbons (ZGNRs) with two antiferromagnetic coupled edges possess PT (combined spatial inversion and time reversal) symmetry and spin double degenerate electronic structures. By breaking PT symmetry via the structure design, we are able to generate spatial spin density in twisted bilayer ZGNRs (TBZGNRs) with different stacking configurations and twisted angles, forming a class of quasi-one dimensional carbon nanoribbon antiferromagnets. We investigate the spin transport in TBZGNRs by employing the non-equilibrium Green's functions method and reveal that the electric current is nonreciprocal and spin-polarized in non-PT symmetric TBZGNRs. Moreover, in PT symmetric TBZGNRs, the spin degenerate can be lifted by applying bias voltage. It shows unique nonreciprocal spin transport with opposite spin-polarization under positive and negative bias voltages. Our results indicate that TBZGNRs should be useful carbon-based materials exhibiting antiferromagnetic order and spin-polarized transport. Thus, this work provides a strategy to achieve spin transport in graphene nanoribbons and carbon-based spintronics via the structural design.