Cu NMR and NQR Studies of High-Tc Superconductor La2-xSrxCuO4

Result of extensive Cu NMR and NQR studies in the superconducting La2-x Srx,CuO4 with x=0.075∼0.24 have been presented. The rapid decrease of the nuclear spin-lattice relaxation rate, 1/T1, and the spin Knight shift below Tc confirm microscopically the existence of the superconducting phase with lower Tc than 38 K for 0.10≤x0.24. For x=0.10, magnetic anomalies emerge at low-T in some small parts of the sample, e.g. T-independent T1 and broadening of spectrum, having some relevance to the magnetic order in La2-xBaxCuO4 with x=0.125. For x>0.15 the T1, T-const, behavior and the existence of the residual spin Knight shift far below Tc have revealed that the superconductivity is of a gapless type with a finite density of states at the Fermi level caused by the mixture of different structures, i.e. tetragonal and orthorhombic. La2-xSrxCuO4, high-Tc superconductivity, Cu nmr and nqr, d-wave gapless superconductivity, antiferromagnetic spin correlation, structural instability.