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

We present elastic and inelastic neutron-scattering results on highly oxygen-ordered YBa2Cu3O6.5 ortho-II. We find no evidence of the presence of long-ranged ordered magnetic moments to a sensitivity of similar to0.003mu(B), 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 rules out the existence of well-correlated static DDW currents in our crystal. 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, similar to6 meV. Our results are only compatible with the coexistence of superconductivity and orbital currents if the latter are dynamic and do not participate in a sharp phase transition to a highly ordered DDW state.