Robust Charge-Density Wave Correlations in Optimally-Doped YBa2Cu3Oy

TL;DR

This study uses NMR to show that static charge-density wave order persists at optimal doping in YBa2Cu3Oy, challenging previous beliefs about its phase boundary and suggesting a more complex interplay with superconductivity.

Contribution

It provides direct NMR evidence of robust CDW correlations at optimal doping, redefining the phase boundary and highlighting disorder and competition effects.

Findings

Static CDW order remains at optimal doping p=0.165

No static CDW detected in overdoped p=0.184 sample

Disorder and competition influence the apparent CDW phase boundary

Abstract

Charge-density wave (CDW) order is a key property of high-Tc cuprates, but its boundaries in the phase diagram and potential connections to other phases remain controversial. We report nuclear magnetic resonance (NMR) measurements in the prototypical cuprate YBa2Cu3Oy demonstrating that short-range static CDW order remains robust at optimal doping (p=0.165), exhibiting a strength and temperature dependence in the normal state similar to those observed at p=0.11 in the underdoped regime. For an overdoped sample with p=0.184, we detect no static CDW down to T=Tc, though weak CDW order plausibly emerges below Tc. More broadly, we argue that both quenched disorder and competition with superconductivity influence the apparent boundary of the CDW phase, likely causing an underestimation of its intrinsic extent in doping. These findings challenge the view that the CDW phase boundary lies below p*=0.19, widely regarded as the critical doping where the pseudogap phase ends in YBa2Cu3Oy.