Band splitting with vanishing spin polarizations in noncentrosymmetric crystals

TL;DR

This paper reports a new band splitting phenomenon in noncentrosymmetric crystals where spin-orbit coupling causes band splitting without net spin polarization, offering potential for spintronic device applications.

Contribution

It introduces the BSVSP phenomenon, classifies point groups into pseudo-polar and non-pseudo-polar, and proposes a method to manipulate spin polarization via electric fields.

Findings

BSVSP occurs in both symmorphic and non-symmorphic systems.

A new classification of point groups is proposed.

A linear magnetoelectric coupling mechanism is introduced.

Abstract

The Dresselhaus and Rashba effects are well-known phenomena in solid-state physics, in which spin-orbit coupling (SOC) splits spin-up and spin-down energy bands of nonmagnetic non-centrosymmetric crystals. Here, we discover a new phenomenon, dubbed as band splitting with vanishing spin polarizations (BSVSP), in which, as usual, SOC splits the energy bands in nonmagnetic non-centrosymmetric systems; surprisingly, however, both split bands show no net spin polarization along certain high-symmetry lines in the Brillouin zone. In order to rationalize this phenomenon, we propose a new classification of point groups into pseudo-polar and non-pseudo-polar groups. By means of first-principles simulations, we demonstrate that BSVSP can take place in both symmorphic (e.g., bulk GaAs) and non-symmorphic systems (e.g., two dimensional ferroelectric SnTe). Furthermore, we propose a novel linear magnetoelectric coupling in reciprocal space, which could be employed to tune the spin polarization with an external electric field. The BSVSP effect and its manipulation could therefore pave a new way to novel spintronic devices.