Spatially Inhomogeneous Competition between Superconductivity and the Charge Density Wave in YBa$_2$Cu$_3$O$_{6.67}$

TL;DR

This study reveals that in underdoped YBCO, regions with ferro-type charge density wave correlations more strongly suppress superconductivity than antiferro-type, indicating inhomogeneous superconducting states influenced by different CDW orderings.

Contribution

The paper demonstrates the spatial inhomogeneity of superconductivity in YBCO related to distinct charge density wave correlations using high-energy x-ray diffraction.

Findings

F-CDW correlations suppress superconductivity more strongly than AF-CDW.

F-CDW has longer-range order capable of modifying electronic structure.

Inhomogeneous superconducting states are linked to CDW correlation types.

Abstract

The charge density wave in the high-temperature superconductor YBa$_2$Cu$_3$O$_{7-x}$ (YBCO) is now known to have two different ordering tendencies differentiated by their $c$-axis correlations. These correspond to ferro- (F-CDW) and antiferro- (AF-CDW) couplings between CDW in neighbouring CuO$_2$ bilayers. This discovery has prompted a number of fundamental questions. For example, how does superconductivity adjust to two competing orders and are either of these orders responsible for the electronic reconstruction? Here we use high-energy x-ray diffraction to study YBa$_2$Cu$_3$O$_{6.67}$ as a function of magnetic field and temperature. We show that regions of the sample with F-CDW correlations suppress superconductivity more strongly than those with AF-CDW correlations. This implies that an inhomogeneous superconducting state exists, in which some regions show a weak or fragile form of superconductivity. By comparison of F-CDW and AF-CDW correlation lengths, it is furthermore concluded that F-CDW ordering is sufficiently long-range to modify the electronic structure. Our study thus suggests that F-CDW correlations have an important impact on superconducting and normal state properties of underdoped YBCO.