Spin Fluctuation Induced Superconductivity Controlled by Orbital Fluctuation

TL;DR

This paper proposes a microscopic model for heavy fermion superconductivity, showing how orbital and spin fluctuations interplay to influence the emergence of different superconducting states, with implications for CeTIn5 compounds.

Contribution

It introduces a Hamiltonian that captures orbital symmetry effects and explains the transition between orbital fluctuation-dominated and spin fluctuation-mediated superconductivity.

Findings

Orbital fluctuations can suppress d-wave superconductivity in degenerate regions.

Increasing crystal field lifts degeneracy, enabling spin fluctuation-mediated superconductivity.

The scenario explains superconductivity behavior in CeTIn5 compounds.

Abstract

A microscopic Hamiltonian reflecting the correct symmetry of $f$-orbitals is proposed to discuss superconductivity in heavy fermion systems. In the orbitally degenerate region in which not only spin fluctuations but also orbital fluctuations develop considerably, cancellation between spin and orbital fluctuations destabilizes $d_{x^{2}-y^{2}}$-wave superconductivity. Entering the non-degenerate region by increasing the crystalline electric field, $d_{x^{2}-y^{2}}$-wave superconductivity mediated by antiferromagnetic spin fluctuations emerges out of the suppression of orbital fluctuations. We argue that the present scenario can be applied to recently discovered superconductors CeTIn$_{5}$ (T=Ir, Rh, and Co).