NMR investigation of the electronic structure of expanded liquid cesium.

Abstract

We describe a comprehensive study of the $^{133}\mathrm{Cs}$ Knight shift and nuclear relaxation rates in liquid cesium from the vicinity of the melting point to the critical region of the liquid-gas transition. The data cover a temperature range 55--1590 \ifmmode^\circ\else\textdegree\fi{}C at pressures up to 90 bars and include a wide range of sample densities from 0.70 to 1.93 g/${\mathrm{cm}}^{3}$. Measurements extended to pressures of 900 bars in the lower part of the temperature range. The data yield the isobaric temperature dependence, the isothermal pressure dependence, and the isochoric temperature dependence of the Knight shift as well as the isobaric temperature dependence of the nuclear relaxation rate. At low densities, a strong enhancement of the Knight shift was observed which is related to enhancement of the static susceptibility. In the range of increasing enhancement of the shift and susceptibility we observed strong deviations of the relaxation rate from the Korringa relation signifying breakdown of the conventional Stoner model of exchange-correlation enhancement. The charge density at the nucleus exhibits a surprising decrease with decreasing density in the range 0.8--1.4 g/${\mathrm{cm}}^{3}$. These effects lead to a description of expanded cesium as a highly correlated metal with incipient antiferromagnetic spin correlations between electrons on neighboring ions.