Thermalization Mediated Ultrafast Excited State Absorption in Few Layer ReS₂

Atomically thin two-dimension materials have emerged as a new class of quantum structures owing to its unique properties such as controllable bandgap, spin valley control, efficient light-electron coupling. Among these, ReS₂ a member of transition metal dichalcogenides (TMDCs) has become the center of research attraction due to its anomalous characteristics, for example, Charge decoupling from extra valence electron of Re atom creates its crystallization in a distorted 1T diamond-like chain structure. Further, the resilient bandgap created by the crystal distortion offers remarkable possibility to produce a large-area ReS₂ possessing properties that are virtually independent of number of layers, in stark contrast to other TMDCs which are prone to out of plane quantum confinement. Despite these benchmark characteristics a comprehensive and profound study of the carrier dynamics in ReS₂ mostly remain unexplored. In the present study using ultrafast pump-probe spectroscopy we have measured the excited state absorption in solution processed few layer ReS₂. The detailed analysis reveals excitation dependent crossover from reverse-saturable absorption to two-photon absorption. Our striking experimental findings show the potential of ReS₂ in optical limiting and switching applications.