TL NMR-STUDY OF TL2BA2CUOX SINGLE-CRYSTALS WITH VARIOUS TC

A number of Tl2Ba2CuOx Single crystals with different T(c)s from 32 to 115 K have been investigated by means of Tl-205 NMR in order to elucidate the possible role of electron spin fluctuations in high-T(c) superconductivity. In the normal state, the spin part of the Knight shift, K(S), has been found to be temperature independent whereas the relaxation time, T1 obeys T1T = a + bT with a increasing and b decreasing as T(c) is lowered. As in other HTCSs a gap between values of T1 and K(s) points to the presence of strong antiferromagnetic correlations. With lowering temperature, T1T reaches a minimum value, which is nearly the same for all crystals, at temperatures 1.3 to 1.5 times higher than T(c). Below the superconducting transition, in crystals with T(c) greater-than-or-equal-to 100 K both K(s) and T1 exhibit a gap-like behaviour with a typical DELTA/T(c) almost-equal-to 3. In crystals with lower T(c)s a residual K(s)(T --> 0) has been found which is most likely related to nuclei lying inside vortex cores.