# Polarity tuning of spin-orbit-induced spin splitting in two-dimensional transition metal dichalcogenides semiconductors

## TL;DR

This study demonstrates that polarity-induced mirror symmetry breaking in monolayer transition metal dichalcogenides enables control over spin splitting and spin relaxation, advancing spintronic device design.

## Contribution

It reveals how polarity tuning via biaxial strain induces in-plane spin splitting and mixed spin states, a novel mechanism for spin control in TMD monolayers.

## Key findings

- Polarity breaking causes in-plane spin polarization.
- Biaxial strain effectively tunes spin splitting.
- Mixed spin states influence spin relaxation mechanisms.

## Abstract

The established spin splitting in monolayer (ML) of transition metal dichalcogenides (TMDs) that is caused by inversion symmetry breaking is dictated by mirror symmetry operations to exhibit fully out-of-plane direction of spin polarization. Through first-principles density functional theory calculations, we show that polarity-induced mirror symmetry breaking leads to new sizable spin splitting having in-plane spin polarization. These splittings are effectively controlled by tuning the polarity using biaxial strain. Furthermore, the admixtures of the out-of-plane and in-plane spin-polarized states in the strained polar systems are identified, which is expected to influence the spin relaxation through the Dyakonov-Perel mechanism. Our study clarified that the polarity-induced mirror symmetry breaking plays an important role in controlling the spin splitting and spin relaxation in the TMDs ML, which is useful for designing future spintronic devices.