Light-induced new collective modes in La${}_{1.905}$Ba${}_{0.095}$CuO${}_4$ superconductor

Abstract

We report near and mid-infrared pump c-axis terahertz probe measurement on a superconducting single crystal La${}_{1.905}$Ba${}_{0.095}$CuO${}_4$ with T${}_c$=32 K. The measurement reveals that the pump-induced change occurs predominantly at the Josephson plasma edge position below T${}_c$. Upon excited by the strong near-infrared pulses, the superconducting state is severely disturbed and incoherent quasiparticle excitations develop in frequency regime above the static plasma edge. However, within very short time delay ($\sim$1.5 ps) we observe the reappearance of a very sharp Josephson plasma edge at frequency lower than the static Josephson plasma edge and the emergence of a new light-induced Josephson mode at higher energy. The results imply that the light can induce new Josephson couplings with different coupling strengths. Similar but weaker effect is observed for the mid-infrared pump. No pump induced effect is detected above T${}_c$.

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