Emergence of light-induced superconducting-like state from the charge density wave state in high-Tc cuprate superconductors

We performed a comprehensive study of light-induced superconducting-like responses in La-based cuprate superconductors, La2-x-yNdySrxCuO4, which exhibit charge stripe orders or a short-range charge density wave (CDW) order depending on the concentration of Nd and Sr, by using near-infrared optical pump and terahertz probe spectroscopy. The light-induced plasma edge was observed in the c-axis terahertz reflectivity for all the samples far above Tc, regardless of long-range stripe or short-range CDW order. Remarkably, the frequency of light-induced plasma edge above Tc coincides with that of Josephson plasma resonance of La2-xSrxCuO4 at the similar doping in the low-temperature superconducting phase, imposing a strong constraint on the interpretation of the phenomenon. We elucidated a close correlation between the emergence of the light-induced c-axis plasma edge and the CDW order or fluctuations in the temperature-doping phase diagram, unveiling the intimate interplay between the equilibrium CDW and the light-induced coherent charge carriers along the c axis in nonequilibrium. The possibility of the existence of incoherent Cooper pairs above Tc that show up upon the photoexcitation is discussed from the optical conductivity analysis.