NMR study of Tl2Ba2CuO6+δ: Antiferromagnetic vortex cores or Bragg glass?

We studied the vortex state of an oriented polycrystalline high-T-c superconductor Tl2Ba2CuO6+delta (T-c similar to 85 K) by Tl-205 NMR spin-echo technique. Although more than 10 years have passed since the sample was synthesized, no aging effects were found in the low-field magnetic susceptibility and the zero-field Cu-63,Cu-65 nuclear quadrupole resonance spectrum. From (TI)-T-205 NMR spectra at 2T, we observed vortex melting, vortex partial melting, imperfect vortex lattices. and the absence of static antiferromagnetic ordering at vortex cores. (c) 2006 Elsevier B.V. All rights reserved.