Nuclear Quadrupole Resonance in (La1-xSrx)2CuO4System

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Abstract
Nuclear quadrupole resonance (NQR) of Cu in (La 1- x Sr x ) 2 CuO 4 system (0.075≦ x ≦0.15) has been performed where the system is transformed from the high- T c superconducting to the normal metallic state. The NQR frequency increases and the spectrum is broadened with increasing x . The nuclear spin-lattice relaxation rate 1/ T 1 shows a remarkable distribution for more than x =0.125. For the nonsuperconducting compound of x =0.15, each component of 1/ T 1 is suppressed as compared to that in the superconducting compound of x =0.075 which is strongly enhanced by antiferromagnetic spin correlation of Cu– d hole, and is found to obey the Korringa relation, T 1 T =const. from 1.4 to 90 K. This dramatic change of 1/ T 1 is accompanied by the disappearance of T c . It is concluded that the superconductivity is realized with the background of the A.F. spin correlation.