Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La$_{2-x}$Ba$_x$CuO$_4$

TL;DR

This study uses time-resolved x-ray scattering to reveal that charge order in La$_{2-x}$Ba$_x$CuO$_4$ is dynamic, overdamped, and exhibits critical scaling, suggesting it may influence superconductivity.

Contribution

It provides direct evidence of the diffusive and critical dynamics of charge order in a cuprate, highlighting its potential role in high-temperature superconductivity.

Findings

Charge order excitations are overdamped and diffusive at 0.4 meV to 2 meV.

Charge order exhibits dynamic critical scaling below 0.4 meV.

Charge order dynamics may participate in superconductivity.

Abstract

Charge order is universal among high-T$_c$ cuprates but its relevance to superconductivity is not established. It is widely believed that, while static order competes with superconductivity, dynamic order may be favorable and even contribute to Cooper pairing. We use time-resolved resonant soft x-ray scattering to study the collective dynamics of the charge order in the prototypical cuprate, La$_{2-x}$Ba$_x$CuO$_4$. We find that, at energy scales $0.4$ meV $ \lesssim \omega \lesssim 2$ meV, the excitations are overdamped and propagate via Brownian-like diffusion. At energy scales below 0.4 meV the charge order exhibits dynamic critical scaling, displaying universal behavior arising from propagation of topological defects. Our study implies that charge order is dynamic, so may participate tangibly in superconductivity.