Hyperfine Interactions and Associated Properties of Alkali Metals

Abstract

The current situation with respect to theory as compared to experiment for the Knight-shifts and relaxation times in alkali metals is reviewed. The roles of the direct spin-density at the nucleus from the conduction electrons, of the exchange core-polarization effect, of the relativistic corrections to the spin-density for the heavier metals, and of the exchange enhancement of suscep- tibility due to electron—electron interactions are discussed in detail. It is shown that through a consideration of all these effects, one is able to obtain good overall agreement with the experimental Knight-shift and relaxation times. However, quantitative agreement with experiment is still lacking, and several additional contributing mechanisms that need to be included, especially core—conduction correlation effects, are briefly discussed. The need for better treatments of exchange enhancement effects on the susceptibility for Bloch electrons and more accurate wave-functions, particularly for the lighter metals lithium, sodium and potassium, is pointed out.