Persistent short-range charge correlations revealed by ultrafast melting of electronic order in YBa$_2$Cu$_3$O$_{6+x}$

TL;DR

This study uses ultrafast X-ray scattering to reveal that in cuprate superconductor YBa2Cu3O6+x, long-range charge density wave order can be transiently destroyed by photo-excitation, leaving behind persistent short-range correlations with distinct dynamics.

Contribution

It demonstrates the ability of ultrafast X-ray scattering to distinguish and analyze coexisting short- and long-range charge correlations in quantum materials.

Findings

Long-range CDW disappears above a threshold fluence.

Short-range CDW persists and appears within 0.2 ps after excitation.

Long-range CDW recovers within 0.6 ps, with partial suppression of peak intensity.

Abstract

Charge density waves (CDW) are ubiquitous in the complex phase diagram of cuprate superconductors and exhibit both short- and long-range correlations. Using time-resolved resonant X-ray scattering, we investigate the photo-induced dynamics of CDW in YBa$_2$Cu$_3$O$_{6.67}$. We discover an excitation threshold ($\Phi$$_\mathrm{C}$ $\approx$ 65 $\mu$J/cm$^2$) above which long-range CDW disappear, revealing a persistent CDW peak with short-range correlation length. Ultrafast photo-excitation promptly uncovers this residual short-range CDW correlations, appearing within $\approx$ 0.2 ps. Long-range CDW coherence recovers within $\approx$ 0.6 ps, while the peak intensity remains partially suppressed. We rationalize the dichotomic behavior in the fluence and temporal dependencies as the signature of two coexisting CDW peaks, arising from short- and long-range correlations, which we disentangle through their distinct response to photo-excitation. We provide evidence that the collapse of long-range correlations is driven by an electronic process, while short-range correlations are characterized by distinct timescales and stiffness against photo-excitation. This approach establishes ultrafast X-ray scattering as an effective tool for disentangling coexisting density waves and correlations in quantum materials.