# Novel attractive pairing interaction in strongly correlated superconductors

## TL;DR

This paper proposes a novel mechanism for superconductivity in strongly correlated materials, where emergent boson fields mediate an attractive interaction leading to s-wave pairing, challenging traditional views on unconventional superconductors.

## Contribution

It introduces a new pairing mechanism mediated by holon gauge fields in mixed valence compounds, expanding understanding of superconductivity beyond electron-phonon interactions.

## Key findings

- Identifies a new attractive interaction mediated by holon fields.
- Predicts s-wave pairing symmetry in strongly correlated systems.
- Provides a self-consistent theory matching experimental observations.

## Abstract

Conventional and unconventional superconductivity, respectively, arise from attractive (electron-phonon) and repulsive (many-body Coulomb) interactions with fixed-sign and sign-reversal pairing symmetries. Although heavy-fermions, cuprates, and pnictides are widely believed to be unconventional superconductors, recent evidence in one of the heavy fermion superconductor (CeCu$_2$Si$_2$) indicate the presence of a novel conventional type pairing symmetry beyond the electron-phonon coupling. We present a new mechanism of attractive potential between electrons, mediated by emergent boson fields (vacuum or holon) in the strongly correlated mixed valence compounds. In the strong coupling limit, localized electron sites are protected from double occupancy, which results in an emergent holon gauge fields. The holon states can, however, attract conduction electrons through valence fluctuation channel, and the resulting doubly occupied states with local and conduction electrons condense as Cooper pairs with onsite, fixed-sign, $s$-wave pairing symmetry. We develop the corresponding self-consistent theory of superconductivity, and compare the results with experiments. Our theory provides a new mechanism of superconductivity whose applicability extends to the wider class of intermetallic/mixed-valence materials and other flat-band metals.