205Tl NMR study of vortex state of Tl2Ba2CuO6+δ

We report a 205Tl NMR study of vortex state for an oriented polycrystalline sample of an overdoped high-Tc superconductor Tl2Ba2CuO6+δ (Tc∼85 K) with magnetic field 2 T along the c-axis. An obvious Redfield pattern of the 205Tl NMR spectrum for our sample at T=5 K indicates the vortex lattice state without local antiferromagnetic order at vortex cores. We emphasize that nonexponential nuclear spin-lattice relaxation curves indicate an imperfect vortex lattice or Bragg glass phase.