Neutron scattering search for static magnetism in oxygen ordered YBa2Cu3O6.5

TL;DR

This study used neutron scattering to search for static magnetic order in oxygen-ordered YBa2Cu3O6.5, finding no evidence of static magnetism or d-density-wave order, but allowing for dynamic orbital currents.

Contribution

The paper provides experimental evidence against static d-density-wave order in YBa2Cu3O6.5, challenging certain theories of orbital currents in high-temperature superconductors.

Findings

No static magnetic moments detected above 0.003 Bohr magnetons.

Absence of sharp elastic peaks indicates no static d-density-wave phase.

Spin susceptibility persists to low energies, suggesting dynamic rather than static orbital currents.

Abstract

We present elastic and inelastic neutron scattering results on highly oxygen ordered YBa2Cu3O6.5 ortho-II. We find no evidence for the presence of ordered magnetic moments to a sensitivity of 0.003 Bohr magnetons, an order of magnitude smaller than has been suggested in theories of orbital or d-density-wave (DDW) currents. The absence of sharp elastic peaks, shows that the d-density-wave phase is not present, at least for the superconductor with the doping of 6.5 and the ordered ortho-II structure. We cannot exclude the possibility that a broad peak may exist with extremely short-range DDW correlations. For less ordered or more doped crystals it is possible that disorder may lead to static magnetism. We have also searched for the large normal state spin gap that is predicted to exist in an ordered DDW phase. Instead of a gap we find that the Q-correlated spin susceptibility persists to the lowest energies studied, 6 meV. Our results are compatible with the coexistence of superconductivity with orbital currents, but only if they are dynamic, and exclude a sharp phase transition to an ordered d-density-wave phase.