X-ray diffraction observation of charge density wave order at zero magnetic field in ortho-II YBa$_2$Cu$_3$O$_{6.54}$

TL;DR

This study uses X-ray diffraction to reveal charge density wave order in ortho-II YBa2Cu3O6.54 at zero magnetic field, showing a specific wavevector and contrasting with high-field measurements, advancing understanding of charge order in cuprates.

Contribution

First direct observation of zero-field charge density wave order in ortho-II YBa2Cu3O6.54 using X-ray diffraction, highlighting differences from high-field studies.

Findings

Charge density wave order exists at zero magnetic field.

The dominant wavevector is (0, 0.328, 0.5), aligned with the chain direction.

Contrasts with high-field NMR results suggesting a different wavevector.

Abstract

X-ray diffraction measurements show that the high-temperature superconductor YBa$_2$Cu$_3$O$_{6.54}$, with ortho-II oxygen order, has charge density wave order (CDW) in the absence of an applied magnetic field. The dominant wavevector of the CDW is $\mathbf{q}_{\mathrm{CDW}} = (0, 0.328(2), 0.5)$, with the in-plane component parallel to the $\mathbf{b}$-axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-II contrast with recent high-field NMR measurements, which suggest a commensurate wavevector along the $\mathbf{a}$-axis. We discuss the relationship between spin and charge correlations in YBa$_2$Cu$_3$O$_{y}$, and recent high-field quantum oscillation, NMR and ultrasound experiments.