Highly persistent spin textures with giant tunable spin splitting in the two-dimensional germanium monochalcogenides

TL;DR

This study predicts and characterizes persistent spin textures with giant, tunable spin splitting in 2D germanium monochalcogenides, highlighting their potential for spintronic applications due to long spin lifetimes and controllable spin orientations.

Contribution

The paper reports the first prediction of PST in 2D GeMC monolayers, demonstrating fully out-of-plane and canted spin textures, and shows tunability of spin splitting via strain.

Findings

PST exists in 2D GeMC around the valence band maximum.

Pure GeX monolayers exhibit out-of-plane PST protected by C2v symmetry.

Janus Ge2XY monolayers show canted PST due to lowered symmetry.

Abstract

The ability to control the spin textures in semiconductors is a fundamental step toward novel spintronic devices, while seeking desirable materials exhibiting persistent spin texture (PST) remains a key challenge. The PST is the property of materials preserving a unidirectional spin orientation in the momentum space, which has been predicted to support an extraordinarily long spin lifetime of carriers. Herein, by using first-principles density functional theory calculations, we report the emergence of the PST in the two-dimensional (2D) germanium monochalcogenides (GeMC). By considering two stable formations of the 2D GeMC, namely the pure GeX and Janus Ge2XY monolayers (X, Y = S, Se, and Te), we observed the PST around the valence band maximum where the spin orientation is enforced by the lower point group symmetry of the crystal. In the case of the pure GeX monolayers, we found that the PST is characterized by fully out-of-plane spin orientation protected by C2v point group, while the canted PST in the y-z plane is observed in the case of the Janus Ge2XY monolayers due to the lowering symmetry into Cs point group. More importantly, we find large spin-orbit coupling (SOC) parameter in which the PST sustains, which could be effectively tuned by in-plane strain. The large SOC parameter observed in the present systems leads to the small wavelength of the spatially periodic mode of the spin polarization, which is promising for short spin channel in the spin Hall transistor devices.