Interdependence of the relaxation of spin and charge degrees of freedom in ferromagnetic AxByMnO3 compounds during the first ten picoseconds after optical excitation

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Three topics will be addressed: Energy relaxation: Pump/probe measurements pertaining to the energy relaxation of the charge carriers in La0.67Ca0.33Mn03 have shown a remarkable decrease of the relaxation rate when the sample temperature is reduced. This observation is tentatively explained with less effective scattering of charge carriers across an energy gap which increases with the magnetization of the sample. Estimates suggest that the k-dependence of the Froehlich interaction of electrons and phonons together with a widening energy gap may account for the observed temperature dependence. This will be tested with more detailed model calculations. Spin relaxation: If the carrier relaxation is dominated by a magnetization gap between spin-split bands, the relaxation across the gap should involve a spin flip. In this case, the early spin relaxation process should slow down concomitant with the energy relaxation when the temperature is decreased. Coherent phonons: Our experimental data exhibit signatures of strongly damped low-frequency coherent phonons. Measurements with improved signal-to noise ration are planned to test the hypothesis that the coherent phonons are associated with Jahn-Teller distortions of the lattice. If this can be verified, more systematic studies promise insight into the interplay of carrier/spin relaxation and lattice dynamics.