Pseudo-spin-gap of (Y,Ca)(Ba,La)2Cu4O8

The temperature dependence of Cu nuclear spin-lattice relaxation rate (T1T)-1 and frequency spectra have been measured in Y1-xCaxBa2Cu4O8 (x=0, 0.05 and 0.075) and YBa2-yLayCu4O8 (y=0.05) by a zero field Cu nuclear quadruple resonance (NQR) spin-echo technique. The carrier doping dependence of pseudo-spin-gap was observed through (T1T)-1 at the planar Cu site but no appreciable change in (T1T)-1 at the chain site Cu. Cation substitution without oxygen deficiency is demonstrated to result in substantial carrier doping on the CuO2 plane