Ultrafast optical probes of dynamic behavior in La$_{0.7}$Sr$_{0.3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-\delta}$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructure

Ultrafast pump-optical probe spectroscopy was used to analyze carriers dynamics behavior in La$_{0.7}$Sr$_{0.3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-\delta}$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructure. Our results show the pump signal $\Delta R/R$ for higher laser power (such as $21$ and $41$ mW), below $T_c$, first goes positive, then crosses zero and goes negative, before relaxing back to equilibrium over a time scale of a few ten picoseconds. We extract the characteristic relaxation time of the different process by fitting the data at these powers with a three-exponential decay. For higher laser power, the long characteristic relaxation time are obtained, which implies the competition between FM order and SC order in the La$_{0.7}$Sr$_{0.3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-\delta}$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructure.