Pseudo Spin-Gap Spectrum in the Monolayer HgBa2CuO4+δ

We report the doping dependence of the planar 63 Cu Knight shift ( 63 K ), the nuclear spin-lattice relaxation rate 63 (1/ T 1 T ) and the Gaussian spin-echo decay rate 63 (1/ T G ) for the high- T c monolayer HgBa 2 CuO 4+δ over a wide doping range [ T c =50, 72, 82 K (underdoping), 96 K (optimal doping) and 30 K (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/ T 1 T can mainly be ascribed to the static one in 1/ T G , and (3) a spin fluctuation amplitude probed by the empirical ratio T 1 T /( T G ) 2 is a monotonic decreasing function of the doping level but not proportional to T c . From comparison with La 2- x Sr x CuO 4 , we discussed the role of the pseudo spin-gap in the high- T c superconductivity.