Structure of Charge Density Waves in La$_{1.875}$Ba$_{0.125}$CuO$_4$

TL;DR

This study reveals how charge density waves in La$_{1.875}$Ba$_{0.125}$CuO$_4$ induce structural distortions that propagate across layers, highlighting the role of weak c-axis screening in interlayer CDW coupling.

Contribution

The paper provides detailed atomic-level insights into CDW-induced distortions and their propagation in cuprates, emphasizing the significance of interlayer interactions.

Findings

CDW induces periodic Cu-Cu spacing modulations within CuO$_2$ planes.

Out-of-plane breathing distortions in La layers are caused by charge ordering.

Structural distortions from CDWs extend across multiple layers due to weak c-axis screening.

Abstract

Although charge-density wave (CDW) correlations exist in several families of cuprate supercon-ductors, they exhibit substantial variation in CDW wavevector and correlation length, indicating a key role for CDW-lattice interactions. We investigated this interaction in La$_{1.875}$Ba$_{0.125}$CuO$_4$ using single crystal x-ray diffraction to collect a large number of CDW peak intensities, and determined the Cu and La/Ba atomic distortions induced by the formation of CDW order. Within the CuO$_2$ planes, the distortions involve a periodic modulation of the Cu-Cu spacing along the direction of the ordering wave vector. The charge ordering within the copper-oxygen layer induces an out-of-plane breathing modulation of the surrounding lanthanum layers, which leads to a related distortion on the adjacent copper-oxygen layer. Our result implies that the CDW-related structural distortions do not remain confined to a single layer but rather propagate an appreciable distance through the crystal. This leads to overlapping structural modulations, in which CuO$_2$ planes exhibit distortions arising from the orthogonal CDWs in adjacent layers as well as distortions from the CDW within the layer itself. We attribute this striking effect to the weak c-axis charge screening in cuprates and suggest this effect could help couple the CDW between adjacent planes in the crystal.