Theory of Field-Induced Phase Transition in PrOs₄Sb₁₂

Abstract

We propose a theory of the field-induced ordered state in PrOs₄Sb₁₂. It is based on an antiferro-quadrupolar (AFQ) interaction in the low-lying singlet–triplet subspace. Using a pseudo-spin description, we clarify a hidden symmetry in the local Hamiltonian and its relation with possible order parameters. Stable AFQ phases are determined for the direction of magnetic fields, and the effect of T_h symmetry on the anisotropic phase diagram is discussed.