# Raman spectrum of 1T'-WTe2 under tensile strain: A first-principles prediction

## TL;DR

This study uses first-principles simulations to predict how tensile strain affects the Raman spectra of monolayer 1T'-WTe2, revealing anisotropic responses and phonon softening at critical strains.

## Contribution

It provides the first theoretical prediction of strain-induced Raman spectral changes and phonon behavior in 1T'-WTe2, highlighting anisotropic effects and critical strain points.

## Key findings

- Phonon branches soften to negative frequencies at specific critical strains.
- Raman shifts of A1g, A3g, and A4g modes show anisotropic responses to strain.
- A3g mode exhibits a parabolic frequency shift with a transition at about 5% strain.

## Abstract

Monolayer WTe2 attracts rapidly growing interests for its large-gap quantum spin Hall effect,which enables promising apllications in flexible logic devices. Due to one-dimensional W-W chains,1T'-WTe2 exhibits unique anisotropic structure and promising properties, which can be modified by simply applying strains. Based on the first-principles simulations, we show that phonon branch undergoes soft down to negative frequency at special q points under different critical strains, i.e., epsilon_a = 11.55 percent along a-axis (with W-W chains) direction, epsilon_b = 7.0 percent along b-axis direction and epsilon_ab = 8.44 percent along biaxial direction. Before each critical strain, the Raman-shift of A1_g, A3_g, and A4_g modes, corresponding to the main peaks in Raman spectra of 1T'-WTe2 , shows anisotropic response to uniaxial strain but most sensitive to biaxial strain. Interestingly, we find that the frequency shift of A3_g mode show parabolic characters of strained 1T'-WTe2, then we split it into two parts and it shows a Raman-shift transition at about 5 percent strains. While for the A1_g and A4_g modes,the frequencies change linearly. Through careful structure and vibration analysis, we try to explain these Raman irregularity in strained 1T'-WTe2.