A Simple Solvable Model for Heavy Fermion Superconductivity from the Two-Fluid Normal State

TL;DR

This paper introduces an exactly solvable momentum-space Kondo-BCS model to explore the transition from weak to strong coupling in heavy fermion superconductivity, revealing a crossover from Fermi liquid to non-Fermi liquid states and novel pairing mechanisms.

Contribution

It presents a new solvable model capturing the crossover from BCS to heavy fermion superconductivity with detailed normal state evolution and dual pairing types.

Findings

Crossover from BCS to heavy fermion superconductivity with increasing Kondo interaction.

Normal state transitions from Fermi liquid to non-Fermi liquid two-fluid state.

Identification of two types of Cooper pairs responsible for strong coupling behaviors.

Abstract

We propose an exactly solvable momentum-space Kondo-BCS model to study heavy fermion superconductivity. The Kondo interaction is local in momentum space, which can be derived from an Anderson lattice with a Hatsugai-Kohmoto interaction between $f$-electrons. By increasing the Kondo interaction, the model exhibits a crossover from a weak-coupling BCS superconductor to a strong-coupling heavy fermion superconductor featured with a large gap ratio and a large specific heat jump anomaly. Accordingly, the normal state evolves from a Fermi liquid above the BCS superconductor to a non-Fermi liquid two-fluid state above the heavy fermion superconductor. The two-fluid normal state also leads to two types of Cooper pairs, one between conduction electrons, the other between composite fermions formed by conduction electrons and $f$-spins, which is responsible for the strong coupling behaviors of heavy fermion superconductivity.