Long-range incommensurate charge fluctuations in (Y,Nd)Ba2Cu3O(6+x)

TL;DR

This study uses resonant soft x-ray scattering to reveal incommensurate charge fluctuations in cuprate superconductors, showing their competition with superconductivity and suggesting an incipient charge-density-wave instability.

Contribution

First direct bulk-sensitive evidence of incommensurate charge fluctuations in (Y,Nd)Ba2Cu3O(6+x), linking them to competing charge-density-wave order in cuprates.

Findings

Charge fluctuations increase upon cooling towards Tc

Charge correlations abruptly decrease below Tc

Evidence suggests a competing charge-density-wave instability

Abstract

There are increasing indications that superconductivity competes with other orders in cuprate superconductors, but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant soft x-ray scattering to identify two-dimensional charge fluctuations with an incommensurate periodicity of $\bf \sim 3.2$ lattice units in the copper-oxide planes of the superconductors (Y,Nd)Ba$_2$Cu$_3$O$_{6+x}$ with hole concentrations $0.09 \leq p \leq 0.13$ per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, $T_c$; further cooling below $T_c$ abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity.