Ultrafast Optical and Magneto-Optical Dynamics in Colossal-Magnetoresistance Manganites

Transient pump-probe reflectance measurements on La$\text{}_{0.67}$Ca$\text{}_{0.33}$MnO$\text{}_{3}$/MgO and La$\text{}_{0.67}$ Ca$\text{}_{0.33}$MnO$\text{}_{3}$/SrTiO$\text{}_{3}$ thin films reveal a hitherto unknown magnetization-dependent energy gap that determines the relaxation process of the optically excited charge carriers on the picosecond time scale. In the case of La$\text{}_{0.67}$Ca$\text{}_{0.33}$MnO$\text{}_{3}$/SrTiO$\text{}_{3}$, the subsequent reflectance dynamics at low temperatures is determined to be substrate-induced strain that drives the sample into a metastable state characterized by an increased number of paramagnetic domains.