Phase Digrams in UPt₃ under Various Field Orientations

Abstract

By numerically analyzing the canonical Ginzburg-Landau (GL) free energy functional with two component order parameters under magnetic fields (H), it is shown that the observed phase diagrams in UPt₃ for both orientations of H⊥ c and H//c in D_6h can be explained consistently. The mysterious field dependence of the unit cell angle of the vortex lattices observed by the neutron scattering experiment is quantitatively reproduced. The predicted diamagnetic term in the above GL turns out to be indispensable to understand these facts. This unambiguously demonstrates that the non-trivial vortex lattices are formed in each domain of temperature and field, reflecting the underlying unconventional pairing symmetry in UPt₃, and strengthening the validity of the canonical GL functional form which is independent of detailed pairing mechanism. Based on the present calculations possible orientational-dependent phase diagrams under pressures are predicted.