Bulk Charge Ordering in the CuO2 Plane of the Cuprate Superconductor YBa2Cu3O6.9 by High-Pressure NMR

Steven Reichardt,Robin Guehne,Michael Jurkutat,Andreas Erb,Jonas Kohlrautz,Jürgen Haase

doi:10.3390/condmat3030023

Abstract

Cuprate superconductors still hold many open questions, and recently, the role of symmetry breaking electronic charge ordering resurfaced in underdoped cuprates as a phenomenon that competes with superconductivity. Here, unambiguous nuclear magnetic resonance (NMR) proof is presented for the existence of local charge ordering in nearly optimally doped YBa2Cu3O6.9, even up to room temperature. Increasing pressure and decreasing temperature leads to the highest degree of order in the sense that the two oxygen atoms of the unit cell of the CuO2 plane develop a charge difference of about 0.02 holes, and order throughout the whole crystal. At ambient conditions, a slightly smaller charge difference and a decreased order is found. Evidence from literature data suggests that this charge ordering is ubiquitous to the CuO2 plane of all cuprates. Thus, the role of charge ordering in the cuprates must be reassessed.

Highlights

Our understanding of the superconducting cuprates still requires development [1]
Cuprate superconductors still hold many open questions, and recently, the role of symmetry breaking electronic charge ordering resurfaced in underdoped cuprates as a phenomenon that competes with superconductivity
Nuclear magnetic resonance (NMR) of Cu and O in the CuO2 plane is very sensitive to the local charge symmetry due to the nuclear quadrupole interaction that measures the electric field gradient (EFG) at each nucleus, and one might expect nuclear magnetic resonance (NMR) to be a versatile, even benchmark, bulk probe for related research

Summary

Introduction

Our understanding of the superconducting cuprates still requires development [1] It is the charge state of their ubiquitous CuO2 plane that triggers a wealth of electronic properties [1,2,3]. Charge ordering in the CuO2 plane and its relation to superconductivity or the pseudogap state was again the focus of research [6,7,8,9,10,11,12,13]. YBa2Cu3O7 and YBa2Cu4O8, appear to be very homogeneous, in the sense that the measured components of the EFGs hardly vary across the CuO2 plane (i.e., one observes very narrow NMR lines for planar Cu and O) in these stoichiometric systems. With a few materials being very homogeneous, the broad featureless lines of all the other systems have usually been dismissed as being related to inhomogeneous doping, impurities, or crystal imperfections

Methods

Results

Conclusion