# Light-induced nonequilibrium response of the superconducting cuprate La$_{2-x}$Sr$_{x}$CuO$_4$

## TL;DR

This study investigates the nonequilibrium dynamics of La$_{2-x}$Sr$_{x}$CuO$_4$ superconductors after photoexcitation, revealing a persistent redshift in Josephson plasma resonance and highlighting the effects of surface heating and analysis artifacts.

## Contribution

It provides new insights into the ultrafast response of cuprate superconductors and discusses potential artifacts in spectral analysis methods.

## Key findings

- Redshift of Josephson plasma resonance persists for hundreds of picoseconds.
- Surface heating explains the metastable spectral features.
- Conventional spectral analysis can introduce artifacts in nonequilibrium measurements.

## Abstract

We report the dynamics of the cuprate superconductor La$_{2-x}$Sr$_{x}$CuO$_4$ ($x = 0.14$) after intense photoexcitation utilizing near-infrared (800 nm) optical pump-terahertz probe spectroscopy. In the superconducting state at 5 K, we observed a redshift of the Josephson plasma resonance that sustains for hundreds of picoseconds after the photoexcitation, indicating the destruction of the $c$-axis superconducting coherence. We show that the metastable spectral features can be described by the photoinduced surface heating of the sample. We also demonstrate that the conventional analysis used to extract the spectra of the photoexcited surface region can give rise to artifacts in the nonequilibrium response.