Copper Nuclear Relaxation Rate and Knight Shift in YBa2Cu4O8

The temperature dependences of the 63Cu nuclear spin-lattice relaxation rate 1/Ti for the Cu(1) chain sites and the planar Cu(2) sites in YBa2Cu4O8 have been measured by nuclear quadrupole resonance(NQR). The in-plane component of the Knight shift for the Cu(2) sites, K21, and the anisotropies of 1/T1 for both sites have been also measured by nuclear magnetic resonance(NMR). In the normal state, 1/T1 for the Cu(2) sites increases rapidly from Tc up to about 250K and behaves approximately T-linearly above 250K. 1/T1 for the Cu(1) sites shows the superlinear temperature dependence. Knight shift K2⊥ increases rapidly with temperature from Tc and saturates above 250K. The anisotropies of 1/T1 for the Cu(1) sites and the Cu(2) sites are ~0.6 and ~3.2, respectively.