Anisotropic Superconductivity Emerging from the Orbital Degrees of Freedom in a $\Gamma_3$ Non-Kramers Doublet System

TL;DR

This paper investigates how orbital degrees of freedom in a three-orbital model for $f^2$ ions lead to anisotropic superconductivity with $E_g$ symmetry, highlighting the role of interorbital interactions and the $ ext{Gamma}_3$ ground state.

Contribution

It demonstrates that interorbital pairing in a $ ext{Gamma}_3$ non-Kramers doublet system can produce an $E_g$ spin-singlet superconducting state, a novel mechanism in such materials.

Findings

$E_g$ spin-singlet superconductivity is stabilized over a wide parameter range.

Interorbital pairing between $ ext{Gamma}_7$ and $ ext{Gamma}_8$ orbitals is key.

Antiferromagnetic interaction stabilizes the $ ext{Gamma}_3$ CEF ground state.

Abstract

We study superconductivity in a three-orbital model for $f^2$ ions with the $\Gamma_3$ crystalline electric field (CEF) ground state. An antiferromagnetic interaction between the $\Gamma_7$ and $\Gamma_8$ orbitals is introduced to stabilize the $\Gamma_3$ CEF state. This interaction also works as an on-site attractive interaction for spin-singlet pairing between electrons in these orbitals. The interorbital pairing state composed of the $\Gamma_7$ and $\Gamma_8$ orbitals on the same site has the $E_g$ symmetry. Indeed, by applying the random phase approximation, we find that the $E_g$ spin-singlet superconducting state is realized over a wide parameter range.