Cu spin dynamics and superconducting precursor effects in planes above Tc in YBa2Cu3O6.7

Spin dynamics at planar sites in oxygen-deficient YBa2Cu3O6+x have been investigated by nuclear spin-lattice relaxation measurements using 63,65Cu nuclear quadrupole resonance and Y89 NMR. A sharp decrease of Cu63 nuclear relaxation below 100 K in YBa2Cu3O6.7 suggests the possible onset of spin pairing in individual planes well above the transition to three-dimensional bulk superconductivity. Comparison of the relaxation rates for the 60-K superconductor YBa2Cu3O6.7 with those of YBa2Cu3O7.0 in the range 100 300 K shows that the planar Cu(2) spin dynamics are strongly affected by changes in carrier concentration.