Ultrafast dynamics of excitons in delafossite CuScO2 thin films

Ultrafast carrier dynamics were investigated in a delafossite CuScO2, a material with a remarkably large binding energy of exciton (∼0.4 eV), using femtosecond transient transmission spectroscopy. Differential transmission spectra showed dispersive structures in the excitonic resonance energies. We have observed a delayed rise-up on a time scale of 10 ps, suggesting slow carrier cooling. It is followed by a slower decay, time constant of which corresponds to the lifetime of exciton (approximately 0.75 ns). These results were analyzed in terms of the generalized many-body Elliott model, accounting for a screening effect of excitons.