Anomalous Reflectivity Oscillation of Layered Manganite La0.5Sr1.5MnO4

We investigate the time-dependent reflectivity of the layered manganite La 0.5 Sr 1.5 MnO 4 at low temperature. We find that the reflectivity oscillates with an anomalously long period, e.g., several tens of hours. The period varies with wavelength and the character of the oscillation depends on the illumination condition. The oscillation is clearly observed below T ∼20 K and almost disappears above this temperature. Furthermore, in the temperature-cycle measurements, the reflectivity oscillation shows a particularly peculiar behavior.