Locally commensurate charge-density wave with three-unit-cell periodicity in YBCO

TL;DR

This study reveals that in YBCO, charge-density waves are locally commensurate with a three-unit-cell period, with long-range incommensurability arising from phase slips, highlighting universal features of CDW in cuprates.

Contribution

It demonstrates that local CDW order in YBCO is unidirectional and commensurate, with long-range incommensurability caused by phase slips, providing insight into the universal nature of CDWs in cuprates.

Findings

Local CDW in YBCO is unidirectional with a period of three unit cells.

Long-range incommensurability is due to phase slips, not a secondary CDW.

CDW has a predominant oxygen character with no evidence of a pair-density wave.

Abstract

In order to identify the mechanism responsible for the formation of charge-density waves (CDW) in cuprate superconductors, it is important to understand which aspects of the CDW's microscopic structure are generic and which are material-dependent. Here, we show that, at the local scale probed by NMR, long-range CDW order in YBa2Cu3Oy is unidirectional with a commensurate period of three unit cells (lambda = 3b), implying that the incommensurability found in X-ray scattering is ensured by phase slips (discommensurations). Furthermore, NMR spectra reveal a predominant oxygen character of the CDW with an out-of-phase relationship between certain lattice sites but no specific signature of a secondary CDW with lambda = 6b associated with a putative pair-density wave. These results shed light on universal aspects of the cuprate CDW. In particular, its spatial profile appears to generically result from the interplay between an incommensurate tendency at long length scales, possibly related to properties of the Fermi surface, and local commensuration effects, due to electron-electron interactions or lock-in to the lattice.