Exotic Multigap Structure in UPt_{3} Unveiled by a First-Principles Analysis.

A heavy-fermion superconductor UPt_{3} is a unique spin-triplet superconductor with multiple superconducting phases. Here, we provide the first report on a first-principles analysis of the microscopic superconducting gap structure. We find that the promising gap structure is an unprecedented E_{2u} state, which is completely different from the previous phenomenological E_{2u} models. Our obtained E_{2u} state has in-plane twofold vertical line nodes on small Fermi surfaces and point nodes with linear dispersion on a large Fermi surface. These peculiar features cannot be explained in the conventional spin 1/2 representation, but is described by the group-theoretical representation of the Cooper pairs in the total angular momentum j=5/2 space. Our findings shed new light on the long-standing problems in the superconductivity of UPt_{3}.