Femtosecond time-resolved dynamics in electron-doped high-Tc superconductor La2-xCexCuO4

The quasiparticle dynamics in the electron-doped high-T-c superconductor La2-xCexCuO4 ( LCCO) was investigated by ultrafast time-resolved optical pump-probe technique. We present results in three temperature regions: namely the low temperature ( T < 0.7 T-c) region, that around T-c (0.7 T-c <= T <= T-c) and the high temperature ( T > T-c) region. In general, there was a slowdown of the relaxation as the temperature decreases. However, the quasiparticle lifetime was found to exhibit a quasi-divergence as the temperature approached T-c from below. The relaxation time in normal state was much longer than what was expected for metallic relaxation, indicating the presence of a T-independent pseudogap. We have also observed picosecond rise component of photoinduced change in reflectivity Delta R/R in the electron-doped LCCO, which is attributed to the Cooper pair-breaking dynamics. The rise time became shorter as the temperature increased. The experimental results are analyzed by Rothwarf-Taylor model.