Phase Diagram and Vortex Structures in UPt₃

Abstract

Possible vortex lattice structures for UPt 3 are investigated for the superconducting order parameter described by a triplet pairing function belonging to a one-dimensional representation. The phase diagram in H vs T for H parallel to the hexagonal c -axis is analyzed. Several observed characteristics, including the existence of four second order transition lines and a tetracritical point are reproduced to confirm the identification of the above pairing state for UPt 3 , which enables us to fully characterize various phases in the presence of H . Additional first order transitions at low H is suggested to occur for an appropriate parameter region.