Two-Dimensional Geometry of Spin Excitations in the High Temperature Superconductor YBa2Cu3O6+x

TL;DR

This study uses neutron scattering to show that magnetic excitations in YBa2Cu3O6+x are two-dimensional, challenging stripe-based theories of high-temperature superconductivity and suggesting liquid-crystalline stripe order instead.

Contribution

The paper provides the first direct neutron scattering evidence that magnetic fluctuations in YBa2Cu3O6+x are two-dimensional, refuting the stripe model's one-dimensional assumption.

Findings

Magnetic fluctuations are two-dimensional in YBa2Cu3O6+x.

Rigid stripe arrays are unlikely across various doping levels.

Data may support liquid-crystalline stripe order.

Abstract

The fundamental building block of the copper oxide superconductors is a Cu4O4 square plaquette. In most of these materials, the plaquettes are slightly distorted and form a rectangular lattice. An influential theory predicts that high-temperature superconductivity is nucleated in "stripes" aligned along one of the axes of this lattice. This theory had received strong support from experiments that appeared to indicate a one-dimensional character of the magnetic excitations in the high temperature superconductor YBa2Cu3O6.6. Here we report neutron scattering data on "untwinned" YBa2Cu3O6+x crystals, in which the orientation of the rectangular lattice is maintained throughout the entire volume. Contrary to the earlier claim, we demonstrate that the geometry of the magnetic fluctuations is two-dimensional. Rigid stripe arrays therefore appear to be ruled out over a wide range of doping levels in YBa2Cu3O6+x, but the data may be consistent with liquid-crystalline stripe order.