Pseudo spin-gap spectrum in the monolayer HgBa2CuO4+δ

We report the doping dependence of the planar Cu-63 Knight shift (K-63), the nuclear spin-lattice relaxation rate (63)(1/T1T) and the Gaussian spin-echo decay rate (63)(1/T-G) for the high-T-c monolayer HgBa2CuO4+delta over a wide doping range [T-c=50, 72, 82 K (underdoping), 96 K (optimal doping) and 30K (overdoping)], measured by the Cu NMR spin-echo technique. We found the following new facts; (1) both the static and the dynamical spin susceptibilities exhibit the pseudo spin-gap behavior over a wide q region around the staggered mode Q, (2) the dynamical pseudo spin-gap in 1/T1T can mainly be ascribed to the static one in 1/T-G, and (3) a spin fluctuation amplitude probed by the empirical ratio T1T/(T-G)(2) is a monotonic decreasing function of the doping level but not proportional to T-c. From comparison with La2-xSrxCuO4, we discussed the role of the pseudo spin-gap in the high-T-c superconductivity.