Unconventional superconductivity from crystal field fluctuations

TL;DR

This paper proposes a new pairing mechanism for superconductivity driven by crystal field fluctuations, which can explain d-wave pairing in cuprates without relying on magnetic interactions.

Contribution

It introduces a novel anisotropic interaction from crystal field fluctuations as a mechanism for superconductivity in strongly correlated systems, especially cuprates.

Findings

The interaction is attractive in charge transfer insulators like cuprates.

A simple model reproduces the d-wave superconducting gap.

The mechanism operates independently of antiferromagnetic exchange.

Abstract

We present a novel pairing mechanism for superconductivity in strongly correlated electron systems, which often have both localised and itinerant charge carriers. An effective anisotropic interaction between the itinerant particles originates from the fluctuations in the crystal field associated with virtual hopping of the localised particles, a process that is also responsible for the Kondo exchange. Interestingly, this interaction is \emph{attractive} for charge transfer insulators such as cuprates. Considering a simple toy model for cuprates, without the antiferromagnetic exchange, this interaction leads to the correct d-wave superconducting gap, thus demonstrating its relevance.