# Probing the uniaxial strain-dependent valley drift and Berry curvature in monolayer MoSi$_2$N$_4$

## TL;DR

This study uses ab initio calculations and theoretical analysis to explore how uniaxial strain affects valley drift and Berry curvature in monolayer MoSi$_2$N$_4$, revealing strain-dependent control of valley and optical properties.

## Contribution

It provides new insights into strain-induced valley and Berry curvature modifications in monolayer MoSi$_2$N$_4$, highlighting the importance of microscopic orbital interactions and symmetry effects.

## Key findings

- Valley drift is significantly affected by uniaxial strain.
- Berry curvature dipole is enhanced under tensile strain.
- Circular polarization degree can be reduced to ~0.98 due to strain effects.

## Abstract

We use ab initio calculations and theoretical analysis to investigate the influence of in-plane strain field on valley drifts and Berry curvatures in the monolayer MoSi$_2$N$_4$, a prototypical septuple atomic layered two-dimensional material. The low energy electron and hole valleys drift far off the K/K' point under uniaxial strains. The direction and strength of valley drift strongly depend on the nature of the charge carrier and uniaxial strain with a more substantial response along the zigzag path. Our findings are governed by the interplay between microscopic orbital contribution and symmetry lowering. The changing geometric properties of Bloch states affect the Berry curvatures and circular dichroism. Specifically, Berry curvature dipole is significantly enhanced under the tensile strain along armchair and zigzag directions. Meanwhile, the particle-hole asymmetry arising from non-equivalent electron and hole valley drifts relax the selection rules, thus reducing the degree of circular polarization up to ~0.98. Therefore, strain engineering of valley physics in the monolayer MoSi$_2$N$_4$ is of prime importance for valleytronics.