A time-resolved optical study of the paramagnetic dielectric-ferromagnetic metal transition in La0.7Ca0.3MnO3

Abstract

The relaxation dynamics of charge carriers in an epitaxial La0.7Ca0.3MnO3 film was studied by the light reflection method with a femtosecond time resolution in a wide temperature range. The relaxation of time-resolved photoinduced reflections was shown to be two-component in the whole temperature range including the paramagnetic dielectric-ferromagnetic metal transition at T ≈ 150 160 K. The fast relaxation component had a maximum lifetime (τ ~ 500 ps) in the transition region, and its contribution to relaxation increased as temperature decreased. The lifetime of the slow component was minimum (τ ~ 15 fs) in the transition region. In addition, fast oscillations assigned to coherent phonons appeared in photoinduced responses at T < 200 K. The dephasing time of these oscillations increased as temperature decreased, whereas their frequency changed insignificantly.