# Raman scattering study of large magnetoresistance semimetals TaAs$_2$ and NbAs$_2$

## TL;DR

This study uses Raman scattering to analyze lattice vibrations and electron-phonon interactions in TaAs$_2$ and NbAs$_2$, which exhibit extremely large magnetoresistance, providing insights into their fundamental properties.

## Contribution

It offers detailed symmetry analysis, mode assignment, and electron-phonon coupling estimates for TaAs$_2$ and NbAs$_2$, advancing understanding of their lattice dynamics and magnetoresistance.

## Key findings

- All Raman active modes observed and assigned.
- Symmetry of modes verified through intensity modulation.
- Electron-phonon coupling is relatively small.

## Abstract

We have performed polarized and temperature-dependent Raman scattering measurements on extremely large magnetoresitance compounds TaAs$_2$ and NbAs$_2$. In both crystals, all the Raman active modes, including six A$_g$ modes and three B$_g$ modes, are clearly observed and well assigned with the combination of symmetry analysis and first-principles calculations. The well-resolved periodic intensity modulations of the observed modes with rotating crystal orientations, verify the symmetry of each assigned mode and are fitted to experimentally determine the elements of Raman tensor matrixes. The broadening of two A$_g$ modes seen in both compounds allows us to estimate electron-phonon coupling constant, which suggests a relatively small electron-phonon coupling in the semimetals TaAs$_2$ and NbAs$_2$. The present study provides the fundamental lattice dynamics information on TaAs$_2$ and NbAs$_2$ and may shed light on the understanding of their extraordinary large magnetoresistance.