# Optical evidence of type-II Weyl semimetals MoTe$_2$ and WTe$_2$

## TL;DR

This study provides optical evidence supporting the classification of MoTe$_2$ and WTe$_2$ as type-II Weyl semimetals by analyzing their temperature-dependent carrier dynamics and electronic structures.

## Contribution

It offers the first optical spectroscopy evidence of type-II Weyl semimetals, revealing two types of carriers and their temperature-dependent behaviors in MoTe$_2$ and WTe$_2$.

## Key findings

- Observation of two Drude peaks indicating different carrier types.
- Temperature dependence of narrow Drude peak suggests Weyl band Dirac carriers.
- Optical spectra align with band structure calculations including electron correlation effects.

## Abstract

The carrier dynamics and electronic structures of type-II Weyl semimetal candidates MoTe$_2$ and WTe$_2$ have been investigated by using temperature-dependent optical conductivity [$\sigma(\omega)$] spectra. Two kinds of Drude peaks (narrow and broad) have been separately observed. The width of the broad Drude peak increases with elevating temperature above the Debye temperature of about 130 K in the same way as those of normal metals, on the other hand, the narrow Drude peak becomes visible below 80 K and the width is rapidly suppressed with decreasing temperature. Because the temperature dependence of the narrow Drude peak is similar to that of a type-I Weyl semimetal TaAs, it was concluded to originate from Dirac carriers of Weyl bands. The result suggests that the conductance has the contribution of two kinds of carriers, normal semimetallic and Dirac carriers, and this observation is an evidence of type-II Weyl semimetals of MoTe$_2$ and WTe$_2$. The obtained $\sigma(\omega)$ spectra in the interband transition region can be explained by band structure calculations with a band renormalization owing to electron correlation.