TRANSVERSE RELAXATION OF CU NUCLEAR SPINS IN YBA2CU3O6.98

We have measured the transverse relaxation of the planar Cu(2) nuclear spins in an oriented powder sample of YBa2Cu3O6.98 (TC=92 K) by using the nuclear quadrupole resonance (NQR) technique. Above Tc, after subtraction of the T1 process, the spin echo envelope decay follows a Gaussian form, and its time constant is almost indepen-dent of temperature. In the vicinity of Tc, however, the Gaussian line shape is gradually narrowed. The calculated value (TG= 149 µsec) for the Gaussian time constant based on the direct nuclear dipole-dipole interaction is comparable to the experimental one (TG = 131±2 µsec) at 297 K. Hence, the nuclear indirect coupling proposed previously may not be needed. Below Tc, the Gaussian line shape was found to be narrowed depending on H1 and especially, it is sharply narrowed at 35 K and 87 K. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.