Phase diagram for the spin pseudogap inLaBa2Cu3Oystudied by NMR

Abstract

The carrier concentration dependence of the spin pseudogap phenomenon in ${\mathrm{LaBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{y}}$ has been studied by means of the NMR/NQR method. From the T dependence of 1/${\mathrm{T}}_{1}$T of the planar Cu site, it has turned out that the characteristic temperature for the spin pseudogap at the staggered mode is a monotonic function of hole concentration in the lightly doped region. However, a spin-gap-like behavior was observed even in the optimally doped sample (y=6.96), where the maximal superconducting transition temperature (${\mathrm{T}}_{\mathrm{c}}$) is realized as a function of hole doping. This feature is quite different from that in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{y}}$, where the spin pseudogap is restricted to the lightly doped region and is not observed in the optimally doped sample (y=6.98). Together with 1/${\mathrm{T}}_{2\mathrm{G}}$ and Knight shift data, the nature of the gap is discussed.