Photoinduced Interlayer Dynamics in T$_d$-MoTe$_2$: A Broadband Pump-Probe Study

TL;DR

This study uses broadband pump-probe spectroscopy to investigate ultrafast electronic and phononic dynamics in T$_d$-MoTe$_2$, revealing gradual spectral changes without a sharp phase transition and significant phonon-induced interband renormalization.

Contribution

It provides the first detailed broadband transient reflectivity analysis of T$_d$-MoTe$_2$, showing continuous evolution of electronic and phononic features under photoexcitation without threshold behavior.

Findings

No evidence of a threshold-like phase transition under photoexcitation.

Large redshift of interlayer phonon spectral features indicating strong interband renormalization.

Gradual evolution of electronic and phononic spectra with pump fluence.

Abstract

We report on time-resolved broadband transient reflectivity (tr-bb-TR) measurements performed on a bulk single crystal of T$_d$-MoTe$_2$ as a function of the incident pump fluence (F). Tr-bb-TR data unveil photoinduced electronic changes progressing on the sub-picosecond timescale as well as the dynamics of the coherent low-frequency $^1A_1$ interlayer shear phonon. Our results indicate a gradual evolution of both the TR and the $^1A_1$ Fourier intensity spectra as a function of F, ruling out the threshold-like change that has been associated with the ultrafast photoinduced $T_d \to 1T'$ phase transition. We also observe a large redshift of the $^1A_1$ Fourier spectral features, which suggests that large renormalization effects are taking place on interband transitions that are dielectrically susceptible to the $^1A_1$ interlayer phonon displacement.