| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 97 === In this thesis, we have prepared La0.85Ca0.15MnO3 thin films by pulsed laser deposition, and have measured the transient reflectivity change ΔR/R as a function of a pump-probe delay at various temperatures. We analyze the amplitude of picosecond fast relaxation behavior at various temperatures. Above the charge ordering temperature TCO, we observe the similar temperature dependence between the amplitude of the fast component and the correlated polaron population. This result is consistent with that of La0.7Ca0.3MnO3 case, which we reported previously. Below TCO, the temperature dependence of the amplitude are similar to that of the charge ordering superlattice peak intensity, which is consistent with the results of Nd0.5Sr0.5MnO3 reported by K. Miyasaka et al. In addition, we analyze the relaxation time of the fast component, which corresponds to the strength of charge ordering. Above TC, the relaxation time is weakly temperature dependent. On the other hand, below TC, the charge ordering mechanism are suppressed by the prevailing of ferromagnetism, so the recovery time (relaxation time) is slow. Below TCO, the charge ordering mechanism is stronger, so the recovery time becomes faster.
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