Local nodal Cooper pairs in multiorbital systems

TL;DR

This paper introduces a new class of multiorbital superconductivity characterized by local Cooper pairs with specific symmetry, arising from strong inter-orbital attractions and exhibiting nodal gaps in certain local ground states.

Contribution

It proposes a novel mechanism for superconductivity in multiorbital systems based on local pairing and negative-U physics, supported by a simple two-orbital model.

Findings

Superconductivity mediated by onsite inter-orbital attractions.

Nodal gaps appear when local ground states are anisotropic.

Relevance to specific heavy fermion compounds.

Abstract

We show the emergence of a new class of superconductivity in multiorbital systems, focusing on non-Kramers f$^2$ states. The Cooper pairs in this class of superconductivity mainly consist of local pairs with the same symmetry as the local f$^2$ ground states. When the local ground state is an anisotropic representation, the superconducting gap has nodes on the Fermi surface. This nodal superconductivity is mediated by the strong onsite inter-orbital attractions as a consequence of negative-$U$ physics generalized to multiorbital systems. We show that this is indeed realized in a simple two-orbital model with antiferro Hund's coupling and enhanced inter-orbital interaction derived via a systematic local down folding. Finally, we briefly discuss superconductivity in Pr-1-2-20 compounds, UBe$_{13}$, and PrOs$_4$Sb$_{12}$ in view of the present mechanism.