Evidence for photoinduced sliding of the charge-order condensate in La$_{1.875}$Ba$_{0.125}$CuO$_4$

TL;DR

This study demonstrates that ultrafast optical pulses can induce a transient sliding state of charge order in La$_{1.875}$Ba$_{0.125}$CuO$_4$, revealing new dynamics of charge density waves in high-temperature superconductors.

Contribution

It provides direct experimental evidence of photoinduced sliding of charge-order condensates using femtosecond soft x-ray scattering.

Findings

Observation of a short-lived nonequilibrium state with shifted wave vector.

Detection of Doppler-like energy shifts indicating sliding motion.

Wave vector change follows pump propagation direction.

Abstract

We use femtosecond resonant soft x-ray scattering to measure the ultrafast optical melting of charge-order correlations in La$_{1.875}$Ba$_{0.125}$CuO$_4$. By analyzing both the energy-resolved and energy-integrated order parameter dynamics, we find evidence of a short-lived nonequilibrium state, whose features are compatible with a sliding charge density wave coherently set in motion by the pump. This transient state exhibits shifts in both the quasielastic line energy and its wave vector, as expected from a classical Doppler effect. The wave vector change is indeed found to directly follow the pump propagation direction. These results demonstrate the existence of sliding charge order behavior in an unconventional charge density wave system and underscore the power of ultrafast optical excitation as a tool to coherently manipulate electronic condensates.