The Triplet Resonating Valence Bond State and Superconductivity in Hund's Metals

TL;DR

This paper proposes that a spin-triplet resonating valence bond state driven by Hund's interactions can serve as a parent for triplet superconductivity in iron-based superconductors, offering a new perspective on unconventional pairing mechanisms.

Contribution

It introduces the concept of a spin-triplet RVB state in Hund's metals as a novel parent state for triplet superconductivity, expanding the understanding of pairing in strongly correlated systems.

Findings

Strong onsite Hund's interactions induce intra-atomic tRVBs in iron-based superconductors.

Doping enables inter-orbital triplets to delocalize and form a fully gapped triplet superconductor.

Predicted staggered onsite pair correlations could be detected via scanning tunnelling Josephson microscopy.

Abstract

A central idea in strongly correlated systems is that doping a Mott insulator leads to a superconductor by transforming the resonating valence bonds (RVBs) into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB) state, driven by spatially, or orbitally anisotropic ferromagnetic interactions can provide the parent state for triplet superconductivity. We apply this idea to the iron-based superconductors, arguing that strong onsite Hund's interactions develop intra-atomic tRVBs between the t$_{2g}$ orbitals. On doping, the presence of two iron atoms per unit cell allows these inter-orbital triplets to coherently delocalize onto the Fermi surface, forming a fully gapped triplet superconductor. This mechanism gives rise to a unique staggered structure of onsite pair correlations, detectable as an alternating $\pi$ phase shift in a scanning tunnelling Josephson microscope.