Ultrafast electronic relaxation dynamics in a valence fluctuation material Sm0.83Y0.17S

We report ultrafast electronic relaxation dynamics of yttrium-doped samarium monosulfide, Sm0.83Y0.17S, which is one of valence fluctuating compounds, by pump-probe measurements. We observed a large increase of the Drude weight in the reflectivity spectrum by the photo-excitation and a double exponential decay of the relaxation time to a metastable state. This suggests that the photo-induced effect can be explained as the change of carrier density. The metastable state has a long lifetime ( > 1 ns) and the carrier density is slightly higher than that before the photo-excitation.