Enhanced ultrafast relaxation rate in the Weyl semimetal phase of $\mathbf{MoTe_2}$ measured by time-and angle-resolved photoelectron spectroscopy

TL;DR

This study uses time- and angle-resolved photoelectron spectroscopy to reveal that the Weyl semimetal phase of MoTe2 exhibits an enhanced ultrafast electron relaxation rate, indicating local gap closure at Weyl points.

Contribution

It demonstrates that tr-ARPES can detect subtle changes in unoccupied band structures associated with topological phase transitions in MoTe2.

Findings

Enhanced relaxation rate in WSM phase of MoTe2

Slower, temperature-independent dynamics in WTe2

tr-ARPES sensitivity to topological phase transitions

Abstract

$\mathrm{MoTe_2}$ has recently been shown to realize in its low-temperature phase the type-II Weyl semimetal (WSM). We investigated by time- and angle- resolved photoelectron spectroscopy (tr-ARPES) the possible influence of the Weyl points in the electron dynamics above the Fermi level $\mathrm{E_F}$, by comparing the ultrafast response of $\mathrm{MoTe_2}$ in the trivial and topological phases. In the low-temperature WSM phase, we report an enhanced relaxation rate of electrons optically excited to the conduction band, which we interpret as a fingerprint of the local gap closure when Weyl points form. By contrast, we find that the electron dynamics of the related compound $\mathrm{WTe_2}$ is slower and temperature-independent, consistent with a topologically trivial nature of this material. Our results shows that tr-ARPES is sensitive to the small modifications of the unoccupied band structure accompanying the structural and topological phase transition of $\mathrm{MoTe_2}$.