Nonlinear optical response and quantum critical phase control in orbital-ordered oxides

在1.6 eV的光子能量下，通过泵浦-探测测量，研究了La2-2xSr1+2xMn2O7(x=0.38)双层锰氧化物单晶的光诱导效应。在铁磁金属状态下，当慢弛豫时间为100ps时，在T_c=127K以下观察到明显的正增长，表明反射率随慢弛豫时间常数的变化是由激光加热引起的。我们还观察到了一个非常规的快速弛豫分量，它的时间常数约为10ps。研究了双层锰氧化物La_&lt；2-2x&gt；sr_&lt；1+2x&gt；Mn_2O_7(x=0.36)的霍尔电阻率和磁化强度。霍尔电阻率表明，在低于50K的低温下，普通霍尔系数和反常霍尔系数都有增加，在这一区域，在1mT的低磁场中已经发现了自旋玻璃态的实验证据。与磁态有关的霍尔电阻率反常行为的根源可能在于准二维电子系统的本征微观不均匀性。

Photoinduced effects in a single crystal of bilayered manganites, La_2-2xSr_1+2xMn_2O_7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6 eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of 100 ps was observed just below Tc=127 K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of 10 ps. This fast relaxing component, whose absolute value has an asymmetric peak at Tc, is presumably due to short-range correlation of Jahn-Teller distortion.The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La_<2-2x>Sr_<1+2x>Mn_2O_7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50 K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system.