Correlation Between the Anomalous Pressure Dependence of the Superconducting Transition Temperature in Thallium and the Temperature Dependence of its Knight Shift

A study of the Knight shift has been carried out on a single crystal of thallium. The isotropic Knight shift decreases with increasing temperature, showing a nonlinear variation which is most pronounced between 50 and 150 K. This behavior is correlated with the anomalous pressure dependence of the superconducting transition temperature at low pressure. From the superconducting data on pure Tl and Tl–Hg alloys, we extract the volume dependence of the electronic density of states, and use it to derive the temperature dependence of the Knight shift. The results agree with the observed data.