Double-Exchange Ferromagnetism and Orbital-Fluctuation-Induced Superconductivity in Cubic Uranium Compounds

Abstract

A double-exchange mechanism for the emergence of ferromagnetism in cubic uranium compounds is proposed on the basis of a j–j coupling scheme. The idea is orbital-dependent duality of 5f electrons concerning itinerant Γ₈⁻ and localized Γ₇⁻ states in the cubic structure. Since orbital degree of freedom is still active in the ferromagnetic phase, orbital-related quantum critical phenomenon is expected to appear. In fact, odd-parity p-wave pairing compatible with ferromagnetism is found in the vicinity of an orbital ordered phase. Furthermore, even-parity d-wave pairing with significant odd-frequency components is obtained. A possibility to observe such exotic superconductivity in manganites is also discussed briefly.