NMR study of high-TC superconductors

Abstract Recent NMR study of high-Tc superconductors carried out by Osaka group is reviewed. NQR frequency vQ, Knight shift K, T1 of 63Cu and 17O were measured over a wide hole doping range from light- to heavy-doped systems, LSCO, YBCO, HBCCO, BSCCO, TBCCO and TBCO, together with impurity and pressure effect. By analysing vQ, K and T1, the local hole numbers of Cu and O at the CuO2 plane, n(Cu) and n(O) the relative magnitude of the uniform susceptibility, χ0 and the low-frequency component of the antiferromagnetic spin fluctuations (AFSF), χQ/Γ (χQ is the staggered susceptibility and Γ is the characteristic energy of the spin fluctuation at q = 0) are obtained. The relation between n(Cu) n(O) and χQ, χQ/Γ, ΓC etc. were discussed. There are optimum values of n(Cu)/2n(O) and n(Cu) + 2n(O) to give maximum TC. The NMR results in the superconducting state are well-explained by d-wave pairing model. The result is consistent with the AFSF mediated superconducting model.