Orientational ordering in solid hydrogens with J=1 in the presence of a crystal field

Abstract

A system of quantum linear rotators with quantum rotational angular momentum J=1 in a crystal field is investigated. An equation is derived for the orientational order parameter. The critical parameters, the phase-separation curve, and the line of superheating and supercooling points are found. It is shown that the thermodynamic behavior of a system of linear rotators in the classical case is identical to that of the limiting quantum (J=1) cases studied in this work. For positive crystal fields there is an analogy between orientational phase transitions in a system of rotators with J=1 and phase transformations in a liquid–vapor system. It is shown that states with J>1 radically change the character the phase transitions in the system of rotators: instead of one critical point characteristic for a system of J=1, now there is a line of critical points.