O.M. Vyaselev, N.N. Kolesnikov, M.P.
Kulakov and I.F. Schegolev.
Tl NMR Study of Tl2Ba2CuOx
single crystals with various Tc.
A number of Tl2Ba2CuOx
single crystals with different Tcs from 32 to 115 K have
been investigated by means of 205Tl NMR in order to elucidate
the possible role of electron spin fluctuations in high-Tc
superconductivity. In the normal state, the spin part of the Knight shift,
Ks, has been found to be temperature independent whereas
the relaxation time, T1 obeys T1T=a+bT
with a increasing and b decreasing as Tc
is lowered. As in other HTCSs a gap between values of T1
and Ks points to the presence of strong antiferromagnetic
correlations. With lowering temperature, T 1T
reaches a minimum value, which is nearly the same for all crystals, at
temperatures 1.3 to 1.5 times higher than Tc. Below the
superconducting transition, in crystals with T ³100
K both Ks and T1 exhibit a gap-like
behaviour with a typical D /Tc@
3. In crystals with lower Tcs a residual Ks
(T-->0) has been found which is most likely related to nuclei lying
inside vortex cores.