Phonon Anharmonicity in Bulk $T_d$-MoTe$_2$

TL;DR

This study investigates how anharmonic phonon interactions in bulk $T_d$-MoTe$_2$ influence optical phonon behavior across temperatures, revealing decay processes and phase transition effects relevant to Weyl semimetals.

Contribution

It provides the first detailed temperature-dependent Raman analysis of anharmonic phonon behavior in bulk $T_d$-MoTe$_2$, highlighting phonon decay mechanisms and phase transition signatures.

Findings

All phonon modes redshift linearly with temperature above 100 K.

Nonlinear frequency shifts occur below 100 K due to phonon decay.

Large changes in Raman mode intensity and linewidth near 250 K indicate a structural phase transition.

Abstract

We examine anharmonic contributions to the optical phonon modes in bulk $T_d$-MoTe$_2$ through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Gr\"{u}neisen model. However, below 100 K we observe nonlinear temperature-dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons. Furthermore, the highest frequency Raman modes show large changes in intensity and linewidth near $T\approx 250$ K that correlate well with the $T_d \to 1T^\prime$ structural phase transition. These results suggest that phonon-phonon interactions can dominate anharmonic contributions at low temperatures in bulk $T_d$-MoTe$_2$, an experimental regime that is currently receiving attention in efforts to understand Weyl semimetals.