Photoinduced Charge-Ordering Fluctuation in Wide-Bandwidth La_0.7Sr_0.3MnO₃ Films

Photoinduced effects on the transmission and resistivity in wide-bandwidth manganite La_0.7Sr_0.3MnO₃ films (T_C= 350K) have been investigated at various temperatures in the range of 5--470K by means of the time-resolved pump--probe method. Below T_C, we have observed a negative transmission change ΔTM/TM at 2.54eV and a positive resistivity change Delta R/R under photo-irradiation at excited energy E_exc = 3.20eV. With temperature approaching to T_C, the values of ΔTM/TM and ΔR/R show a significant reduction. We have ascribed the photoinduced changes on the transmission and resistivity of the La_0.7Sr_0.3MnO₃ film to the charge-ordering fluctuation in the ferromagnetic phase, which is similar to that observed in the narrow-bandwidth La_0.7Ca_0.3MnO₃ films.