Anomalous superconductivity and superfluidity in repulsive fermion systems

TL;DR

This paper explores how unconventional superconductivity and superfluidity can arise in fermionic systems with purely repulsive interactions, identifying mechanisms and conditions that enhance critical temperatures across various materials and models.

Contribution

It introduces a comprehensive theoretical framework based on the Kohn-Luttinger mechanism to explain and predict anomalous pairing in repulsive fermion systems, extending to multiple models and materials.

Findings

Superconductivity can occur in repulsive fermion systems via unconventional pairing.

Critical temperature can be significantly increased in spin-polarized or two-band systems.

The theory explains anomalous p-, d-, and f-wave pairing in diverse materials.

Abstract

We discuss the mechanisms of unconventional superconductivity and superfluidity in 3D and 2D fermionic systems with purely repulsive interaction at low densities. We construct phase diagrams of these systems and find the areas of the superconducting state in free space, as well as on the lattice in the framework of the Fermi-gas model with hard-core repulsion, the Hubbard model, the Shubin-Vonsovsky model, and the $t-J$ model. We demonstrate that the critical superconducting temperature can be greatly increased in the spin-polarized case or in a two-band situation already at low densities. The proposed theory is based on the Kohn-Luttinger mechanism or its generalizations and explains or predicts anomalous $p$-, $d$-, and $f$-wave pairing in various materials, such as high-temperature superconductors, the idealized monolayer and bilayer of doped graphene, heavy-fermion systems, layered organic superconductors, superfluid $^3$He, spin-polarized $^3$He mixtures in $^4$He, ultracold quantum gases in magnetic traps, and optical lattices.