Cu NQR Study on Transverse Relaxation Rate below T c in YBa2Cu3O7

Abstract
The transverse relaxation rate T2 -1 was measured in YBa2Cu3O7 from 4.2 to 100 K in zero magnetic field. It showed a sudden drop just below T c down to 1/3 of that above Tc . A cusp-shaped sharp peak of T2 -1 was found at 35 K for Cu(2) (plane) site, but not for Cu(l) (chain) site. Except the peak, all the behavior can be interpreted by the model of Pennington et al. that the origin of T2 -1 at 100 K is mainly the local field fluctuation by the Cu d-electron and secondly the indirect nuclear spin-spin coupling via superexchange interaction between Cu-ions. Below Tc the former is sup-pressed.

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