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

TL;DR

This paper proposes a double-exchange mechanism for ferromagnetism in cubic uranium compounds, highlighting orbital-dependent duality of 5f electrons and predicting orbital-fluctuation-induced superconductivity with unconventional pairing symmetries.

Contribution

It introduces a novel double-exchange model based on a j-j coupling scheme for uranium compounds, linking ferromagnetism and orbital fluctuations to unconventional superconductivity.

Findings

Orbital-dependent duality of 5f electrons in cubic uranium compounds.

Prediction of odd-parity p-wave superconductivity near orbital order.

Identification of even-parity d-wave pairing with odd-frequency components.

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 {\it orbital-dependent duality} of $5f$ electrons concerning itinerant $\Gamma_8^-$ and localized $\Gamma_7^-$ 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.