Charge density waves in YBa$_2$Cu$_3$O$_{6.67}$ probed by resonant x-ray scattering under uniaxial compression

TL;DR

This study investigates how uniaxial compression affects charge density waves in underdoped YBa$_2$Cu$_3$O$_{6.67}$ using resonant x-ray scattering, revealing uniaxial order parameters and the plane-specific nature of 3D charge order.

Contribution

It provides the first detailed analysis of uniaxial pressure effects on 2D and 3D charge correlations in YBa$_2$Cu$_3$O$_{6.67}$, highlighting the uniaxial nature of the order parameter.

Findings

Pressure symmetrically enhances charge correlations along orthogonal directions.

3D charge order is confined to CuO$_2$ planes and is uniaxial.

Charge order is sensitive to uniaxial strain and may be related to electronic nematicity.

Abstract

We report a comprehensive Cu L$_3$-edge resonant x-ray scattering study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped high-temperature superconductor YBa$_2$Cu$_3$O$_{6.67}$ under uniaxial compression up to 1% along the two inequivalent Cu-O-Cu bond directions (a and b) in the CuO$_2$ planes. The pressure response of the 2D charge correlations is symmetric: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic resonant x-ray scattering measurements show that the 3D charge order resides exclusively in the CuO$_2$ planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity.