Tunneling spin current in a system with spin degeneracy

TL;DR

This paper theoretically investigates how spin currents can be generated in PT symmetric band insulators with spin degeneracy, emphasizing the role of the shift vector and tunneling processes under strong electric fields.

Contribution

It identifies the shift vector as essential for spin current generation in PT symmetric systems and demonstrates this through analytical and numerical models.

Findings

Shift vector is necessary for tunneling spin current in PT symmetric insulators.

Nonzero tunneling spin current occurs in spin-degenerate systems with shift vectors.

Numerical models confirm theoretical predictions about spin current generation.

Abstract

We study theoretically spin current generation from a band insulator with PT symmetry, which is associated with Zener tunneling in strong dc electric fields. Each band in this system 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 a PT symmetric system. 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.