Ultrafast optical response in giant magnetoresistance manganites

We measured optical time-resolved photoinduced reflectivity in La0.82Pb0.18MnO3+8 thin film as a function of temperature. The photoinduced signal consists of initial fast relaxation on 200-300 fs scale followed by a slower relaxation on 10-100 ps timescale and extremely slow response on the ns-mus timescale. All components show distinctive changes below metal-insulator transition. Amplitudes of the faster components increase with decreasing temperature below metal-insulator transition indicating a bottleneck in the relaxation. The slow components amplitudes show distinctive peak at similar to 200K indicating presence of localized states in the vicinity of the Fermi energy significantly below the metal-insulator transition.