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

能量弛豫：La0.67Ca0.33Mn03中载流子的能量弛豫的泵浦/探针测量表明，当样品温度降低时，弛豫率显著降低。这一观察结果可以暂时解释为，随着样品磁化强度的增加，载流子在能量间隙中的散射效果较差。估计表明，电子和声子的Froehlich相互作用的k依赖性以及不断扩大的能隙可能解释了观察到的温度依赖性。这将通过更详细的模型计算进行测试。自旋弛豫：如果载流子弛豫是由自旋分裂带之间的磁化间隙主导的，那么穿过间隙的弛豫应该包括自旋翻转。在这种情况下，当温度降低时，早期的自旋弛豫过程会随着能量的弛豫而减慢。相干声子：我们的实验数据显示出强阻尼低频相干声子的特征。利用改进的信噪比进行测量，以验证相干声子与晶格的扬-泰勒扭曲有关的假设。如果这可以被证实，更系统的研究有望深入了解载流子/自旋弛豫和晶格动力学的相互作用。

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.