Photoinduced shortening of metallic bond in 1T-ReS₂ revealed by femtosecond electron diffraction

Rhenium disulfide with a distorted crystal structure has recently attracted tremendous attention for its excitonic and highly anisotropic properties. While ultrafast spectroscopies have extensively probed the carrier response to photoexcitation, the associated lattice response has remained elusive. In this study, we utilize MeV femtosecond electron diffraction to unravel the intricate dynamics of lattice responses and energy flow post-photoexcitation. Combining with structure factor calculations, our investigation reveals the dominance of photoinduced shortening in the Re-Re metallic bond, driven by the strong electron-phonon coupling via the A(g)(8) mode, resulting in an anisotropic intensity change of Bragg reflections within the initial 0.2 ps. Subsequent stretching of the metallic bond, coupled with the concurrent lattice thermalization, enables the system to reach a new equilibrium within 20 ps. This comprehensive understanding of lattice responses in a nonequilibrium state provides unique insights into photoinduced dynamics in 1T '-ReS2 from a structural perspective.