NMR shift behavior of the planar Cu(1) site in the underdoped superconductorHg0.8Re0.2Ba2Ca2Cu3O8+y

Abstract

${}^{63}\mathrm{Cu}$ hyperfine shift (Knight-shift) measurements have been carried out on the trilayered superconductor ${\mathrm{Hg}}_{0.8}{\mathrm{Re}}_{0.2}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{8.3}{(T}_{c}=130\mathrm{K}).$ The temperature dependence of the in-plane Cu(1) Knight shift, for the fourfold oxygen coordinated Cu-O plane, clearly exhibits non-Fermi-liquid behavior. Our data has been placed in the context of the magnetic phase diagram of the nonlinear $\ensuremath{\sigma}$ model, which highlights the various regions of magnetic scaling. In this way, evidence is obtained for the presence of a spin pseudogap in this Hg-based compound. This work also supports the suggestion of a nearly antiferromagnetic (AFM) Fermi liquid that dominates the magnetic shift and relaxation behaviors of the ${}^{63}\mathrm{Cu}$ spins through an isotropic transferred coupling. To test the effects of the AFM enhancements on the Cu(1) spin-lattice relaxation rate, the ratio of the dynamical and static spin susceptibilities derived from relaxation and Knight-shift data is compared to that expected for materials having a transferred coupling of the Cu spins. There is a significant increase in the departure of this ratio from the expected value of 0.53, for an unperturbed transferred coupling scenario, with a drop in temperature below 300 K, suggesting an enhancement in the AFM fluctuations in this temperature region.