DOPING LEVEL DEPENDENCE OF SPIN-GAP BEHAVIOR IN Y(BA1-XLAX)(2)CU3OY STUDIED BY CU-NQR

In order to investigate the hole doping dependence of the spin-gap behavior in Y123 system, the temperature dependence of the nuclear spin-lattice relaxation time T-1 of Cu(2) site was measured in Y(Ba1-xLax)(2) Cu-3 O-y system. The long-range antiferromagnetic ordered states in x greater than or equal to 0.4 confirmed by the Cu(2) NMR signal around 90 MHz ensure that the system is in the lightly doped region, at least in x less than or equal to 0.3. Well-defined spin-gap behaviors were observed at least in x less than or equal to 0.1. Considering the previous result for YBa2CU3O6.63, the spin-gap temperature, T-s, which is defined as the peak temperature in (T1T)(-1)(T), increases linearly with the decrease of the hole content per unit cell in CuO2 sheet, P-sh(X), which was evaluated on the basis of the diagram by Tokura et al. and our results for oxygen content gamma. This result places one restriction on the theoretical model for the spin-gap behavior.