# Strain-induced stripe phase in charge ordered single layer NbSe$_2$

## TL;DR

This study uses ab-initio calculations to explore how strain influences phase transitions between triangular and stripe charge density wave patterns in single-layer NbSe2, revealing strain-induced phase separation and modulation characteristics.

## Contribution

It provides a detailed theoretical analysis of strain-induced structural instabilities and phase separation in pristine single-layer NbSe2, linking strain to specific charge modulation patterns.

## Key findings

- Stripe phase is favored by compressive isotropic strain.
- The wavelength of charge modulation matches experimental observations.
- Phase separation occurs between triangular and stripe phases.

## Abstract

Charge density waves are ubiquitous phenomena in metallic transition metal dichalcogenides. In NbSe$_2$, a triangular $3\times3$ structural modulation is coupled to a charge modulation. Recent experiments reported evidence for a triangular-stripe transition at the surface, due to strain or accidental doping and associated to a $4\times4$ modulation. We employ \textit{ab-initio} calculations to investigate the strain-induced structural instabilities in a pristine single layer and analyse the energy hierarchy of the structural and charge modulations. Our results support the observation of phase separation between triangular and stripe phases in 1H-NbSe$_2$, relating the stripe phase to compressive isotropic strain, favouring the $4\times4$ modulation. The observed wavelength of the charge modulation is also reproduced with good accuracy.