Dominant role of charge ordering on high harmonic generation in Pr0.6Ca0.4MnO3

High harmonic generation (HHG) is a typical high-order nonlinear optical phenomenon and can be used to probe electronic structures of solids. Here, we investigate the temperature dependence of HHG from Pr0.6Ca0.4MnO3 in the range of 7-294 K, including the charge ordering (CO) transition and magnetic transition temperatures. The high harmonic (HH) intensity remains almost constant in the high-temperature charge- disordered phase. However, as the temperature is lowered, it starts to increase near the CO transition temperature where an optical gap related to the CO appears. The anomalous gap energy dependence resembles the one recently reported in a Mott insulator. We attribute the suppression of the HH intensity at high temperatures to the destructive interference among HH emissions from thermally activated multiple charge configurations. Our results suggest that HHG is a promising tool for probing the fluctuation of local order in strongly correlated systems.