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

TL;DR

This study demonstrates that light pulses can induce new collective Josephson modes in a cuprate superconductor, revealing transient modifications of superconducting coupling properties below T_c.

Contribution

It provides direct experimental evidence of light-induced new Josephson modes and couplings in a high-Tc superconductor, a novel insight into light-matter interactions in superconducting states.

Findings

Reappearance of a sharp Josephson plasma edge after excitation

Emergence of a new light-induced Josephson mode at higher energy

No effects observed above T_c

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$.