CARRIER CONCENTRATION DEPENDENCES OF THE NUCLEAR-SPIN-LATTICE RELAXATION RATE AND THE KNIGHT-SHIFT IN Y1-XCAXBA2CU4O8

The temperature dependences of the Cu-63 nuclear spin-lattice relaxati on rate T-1(-1) and the Knight shift K(ab) at the planar Cu(2) site in Ca substituted YBa2Cu4O8 have been measured by the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) techniques. The notation ''ab'' means that the external field is perpendicular to the c-axis. The temperature dependence of K(ab) in the Ca substituted sample becomes weaker compared with the non-substituted sample, indica ting that the electronic state in the CuO2 plane turned more metallic with Ca substitution. On the other hand, (T1T)-1 in the non-substitute d sample increased rapidly with increasing temperature and showed a ma ximum value at 160 K, the so-called spin-pp temperature, T(S). Subsequ ently, (T1T)-1 decreased with increasing temperature above the spin-ga p temperature as in the Curie-Weiss law. While the behaviors of (T1T)- 1 in Ca substituted samples were similar to that in the non-substitute d YBa2Cu4O8, the spin-gap temperature decreased with increasing Ca (ho le carrier) content. From the decrease of T(S) with the carrier concen tration, we conclude to the existence of a negative linear relation be tween the spin-pp temperature and the superconducting transition tempe rature.