Electron spin-lattice relaxation rate in Y(Gd)Ba2Cu4O8: Evidence for d-wave pairing in high-T-c materials

Using an original modulation technique, the longitudinal (spin-lattice) rel axation of the impurity Gd3+ ions has been investigated in the superconduct ing state of Y0.99Gd0.01Ba2Cu4O8 magnetically aligned powders. The results agree well with the linewidth analysis performed on a single crystal. At lo w temperatures (T < 60 K) the relaxation rate T-1(-1) is found to be propor tional to T-3, suggesting d-wave superconducting pairing. The data are cons istent with previous Knight shift (K-Gd) measurements that revealed a linea r temperature dependence of the uniform spin susceptibility. The Korringa r elation between T-1 and K-Gd is confirmed indicating the validity of the Fe rmi-liquid model.