Persistent photogenerated state attained by femtosecond laser irradiation of thin $T_d$-MoTe$_2$

TL;DR

This study demonstrates that femtosecond laser irradiation can induce a persistent, reversible structural change in thin $T_d$-MoTe$_2$, enabling optical control of its topological phase with potential applications in quantum materials.

Contribution

The paper reveals a novel persistent structural state in $T_d$-MoTe$_2$ induced by femtosecond laser irradiation, which can be reversed by further laser treatment, advancing optical control of topological phases.

Findings

Femtosecond laser irradiation causes a persistent disappearance of the shear phonon mode in $T_d$-MoTe$_2$.

The laser-induced structural change withstands annealing up to 500 K.

The structural state can be reverted to the original phase by laser treatment at room temperature.

Abstract

Laser excitation has emerged as a means to expose hidden states of matter and promote phase transitions on demand. Such laser induced transformations are often rendered possible owing to the delivery of spatially and/or temporally manipulated light, carrying energy quanta well above the thermal background. Here, we report time-resolved broadband femtosecond (fs) transient absorption measurements on thin flakes of Weyl semimetal candidate $T_d$-MoTe$_2$ subjected to various levels and schemes of fs-photoexcitation. Our results reveal that impulsive fs-laser irradiation alters the interlayer behavior of the low temperature $T_d$ phase as evidenced by the persistent disappearance of its characteristic coherent $^1$A$_1$ $=$ 13 cm$^{-1}$ shear phonon mode. We found that this structural transformation withstands thermal annealing up to 500 K, although it can be reverted to the 1$T$\' phase by fs-laser treatment at room temperature. Our work opens the door to reversible optical control of topological properties.