High-T$_c$ and Low-T$_c$ Superconductivity in Electron Systems With Repulsion

TL;DR

This paper investigates how purely repulsive electron systems can transition to superconducting states, with phase diagrams showing the influence of Coulomb interactions and impurities on critical temperatures in various materials.

Contribution

It demonstrates the instability of repulsive fermionic systems towards superconductivity and constructs phase diagrams considering long-range interactions and disorder effects.

Findings

Repulsive systems can become superconducting via Kohn-Luttinger mechanism.

Long-range Coulomb interactions can increase critical temperatures.

Disorder and impurities affect superconducting properties in graphene.

Abstract

We demonstrate the instability of the normal state of purely repulsive fermionic systems towards the transition to the Kohn-Luttinger superconducting state. We construct the superconducting phase diagrams of these systems in the framework of the Hubbard and Shubin-Vonsovsky models on the square and hexagonal lattices. We show that an account for the long-range Coulomb interactions, as well as the Kohn- Luttinger renormalizations lead to an increase in the critical superconducting temperatures in various materials, such as high-temperature superconductors, idealized monolayer and bilayer of doped graphene. Additionally, we discuss the role of the structural disorder and the nonmagnetic impurities in superconducting properties of real graphene systems.