Ultrafast photoinduced reflectivity transients in (Nd0.5Sr0.5)MnO3

The temperature dependence of ultrafast photoinduced reflectivity transients is reported in Nd 0 . 5 Sr 0 / 5 MnO 3 thin film. The photoinduced reflectivity shows a complex response with very different temperature dependences on different timescales. The response on the subpicosecond time scale appears to be only weakly sensitive to the 270 K metal-insulator phase transition. Below ∼160 K the subpicosecond response displays a two component behavior indicating inhomogeneity of the film resulting from the substrate-induced strain. On the other hand, the slower response on the 10-100 ps timescale is sensitive only to the metal-insulator phase transition and is in agreement with some previously published results. The difference in the temperature dependences of the responses on nanosecond and microsecond time scales indicates that thermal equilibrium between the different degrees of freedom is established relatively slowly, on a nanosecond time scale.