The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction.

E M Forgan,D Bonn,A K R Briffa,S D Brown,M V Zimmermann,M Hücker,N B Christensen,L Bouchenoire,S M Hayden,W N Hardy,Ruixing Liang,E Blackburn,A T Holmes,J Chang

doi:10.1038/ncomms10064

Abstract

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ∼60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.

Highlights

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear
It is clear that the CDW state is a ubiquitous phenomenon in cuprate high-critical-temperature superconductors, appearing in the underdoped region in both hole-2–15 and electron-doped[16] materials at a temperature higher than Tc, suggesting that the CDW is a characteristic instability of the CuO2 plane
We find that the ionic displacements associated with the CDWs are maximum near the CuO2 bilayers and break their mirror symmetry

Summary

Introduction

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. Experiments on YBCO using resonant soft X-ray scattering suggest that the CDW is associated with significant d-wave components for charges on the oxygen bonds around the Cu site[19,20], as proposed by Sachdev[21] This conclusion is supported by scanning tunnelling microscopy (STM) observations of the surface of Bi2Sr2CaCu2O8 þ x and Ca2 À xNaxCuO2Cl2 We find that the ionic displacements associated with the CDWs are maximum near the CuO2 bilayers and break their mirror symmetry They involve displacements of planar oxygens perpendicular to the layers; these displacements have a strong component with dsymmetry. These results allow a physical understanding of the changes in electronic structure, transport properties and quantum oscillation results in the normal state of this cuprate material that are associated with the CDWs

Methods

Results

Conclusion