I.F. Schegolev, N.N. Kolesnikov, V.N. Kopylov, T.G. Tagonidze, O.M. Vyasilev.
On a possible reason of T_c suppression with oxygen doping in Tl₂Ba₂CuO_6+x.

  Abstract:
Magnetic susceptibility and ⁶³Cu and ²⁰⁵Tl nuclear spin-lattice relaxation rates have been measured in Tl₂Ba₂CuO_6+x high- temperature superconductor to establish the mechanism of decreasing the transition temperature with oxygen doping. The experiments have revealed the presence of localized paramagnetic centers (LPC) whose concentration  grown with increasing oxygen content. These centers can give rise to magnetic scattering of the Cooper pairs and thus be responsible for the T_c suppression. This assumption is supported by the pair-breaking effects observed in the NMR Knight shift and relaxation rate behavior in the superconducting state.