Stability of the light-induced hidden charge density wave state within the phase diagram of 1T−TaS2−xSex

Abstract

The femtosecond transient optical spectroscopy is employed to study the relaxation dynamics of the equilibrium and hidden metastable charge-density-wave states in single crystals of $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ as a function of the Se doping $x$. Similar to pristine $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, the transition to a hidden phase is observed at low temperature after a quench with a single 50 fs laser pulse, in the commensurate Mott phase up to $x=0.6$. The photo-induced hidden-phase formation is accompanied by a notable change in the coherent phonon spectra, and particularly the collective amplitude mode. While the temperature stability of the hidden phase is only slightly dependent on the Se content, the creation-threshold fluence strongly increases with Se content from 1 to $\ensuremath{\sim}4$ mJ/${\mathrm{cm}}^{2}$, which is attributed predominantly to the change in optical absorption coefficient at the laser excitation wavelength, and not an increased barrier of the hidden state with increasing Se.