Nuclear magnetic resonance studies of the linear chain mercury compoundHg2.86AsF6

Abstract

Studies of the nuclear spin-lattice relaxation of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ and the Knight shift of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ in the mercury chain conductor ${\mathrm{Hg}}_{2.86}$As${\mathrm{F}}_6$ are presented. At low temperatures, the relaxation times, $T_1\left({}_{}{}^{19}{}_{}{}^{}\mathrm{F}\right)$ and $T_1\left({}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}\right)$ of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$, respectively, show characteristic metallic behavior with $T_1\left({}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}\right)T=7.5\mathrm{}\times {10}^{-3\mathrm{}}$ sec K and $T_1\left({}_{}{}^{19}{}_{}{}^{}\mathrm{F}\right)T=340\mathrm{}$ sec K at 10 MHz. ${\left[T_1\right({}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}\left)T\right]}^{-1\mathrm{}}$ is found to decrease by ∼45% as the magnetic field is decreased from 13 to 5.6 kOe. The ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ Knight shift is +1.9% and nearly temperature and field independent. The relatively slow relaxation of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ at low temperature indicates that the conduction electrons are primarily localized on the mercury chains. A model band structure for the conduction electrons on the two-dimensional interpenetrating mercury chain structure is considered taking into account the interaction between chains in the $\overrightarrow{\mathrm{a}}$ and $\overrightarrow{\mathrm{b}}$ crystallographic directions. The resulting electronic wave function and the Fermi surface display quasi-one-dimensional properties even for relatively strong interchain coupling. Using this model it is argued that the field dependence of $T_1\left({}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}\right)T$ arises from the long-wavelength low-frequency part of the magnetic susceptibility of this pseudo-one-dimensional metal.