Possible Existence of a Transient Superfluid Plasma in Liquid Helium II

Abstract

Magnetic susceptibility measurements have been made between 4.2 and 1.1 K on single crystals of cerium ethyl sulphate diluted with various amounts of lanthanum ethyl sulphate. It has been observed that the splitting between the ground and first excited levels of the Ce3+ ion varies with the degree of dilution, the levels actually inverting. This is attributed to the change in the crystal field, and a group theory argument is given for a simple model to show that such an inversion of the levels is permissible.