Tunneling spin current in systems with spin degeneracy
Y Suzuki
Abstract
We study theoretically spin current generation from band insulator$\mathsf{s}$ with PT symmetry, which is associated with Zener tunneling in strong dc electric fields. Each band in these systems is doubly degenerate with opposite spins, but spin rotational symmetry is not preserved in general. We consider the condition for spin current generation in connection with the nature of the wave function, which ultimately depends on a geometric quantity known as the shift vector. From an analysis of a two-band model, we find that the shift vector is necessary for spin current generation in PT-symmetric system$\mathsf{s}$. We also present zigzag chain models that have shift vectors, and confirm from numerical calculations that a nonzero tunneling spin current occurs in spin-degenerate systems.