Light-induced switching to a Metastable Phase in a Layered Superconductor La$_{2-x}$Sr$_x$CuO$_4$ (x=0.15)

TL;DR

This study demonstrates that intense optical excitation can induce a long-lived metastable phase in La$_{2-x}$Sr$_x$CuO$_4$, characterized by new collective modes and altered interlayer couplings, revealing photoinduced phase control in high-Tc superconductors.

Contribution

It provides direct experimental evidence of light-induced metastable phases with alternating Josephson couplings in a layered superconductor, expanding understanding of photoinduced phase transitions.

Findings

Observation of a new long-lived longitudinal mode after photoexcitation.

Detection of a metastable phase with alternating interlayer Josephson couplings.

Suppression of superconductivity with increasing photoexcitation intensity.

Abstract

We investigated transient optical responses in an optimally-doped high-Tc superconductor La2-xSrxCuO4 (x=0.15) by using 800-nm optical pump and terahertz probe spectroscopy. With increasing the photoexcitation intensities, the Josephson plasma resonance shows a gradual redshift, indicating the suppression of superconductivity by the photoexcitation. With further increasing the photoexcitation intensities, a new longitudinal mode in the loss function spectrum appears and grows from the high energy side, accompanied by a new transverse mode as manifested in the conductivity spectrum. The observed spectra are described by the multilayer model with alternating interlayer Josephson couplings. The new longitudinal and transverse modes sustain much longer than several hundred picoseconds after the photoexcitation, indicating that the new metastable phase with possessing alternating interlayer Josephson couplings is induced by the strong photoexcitation.