Competition of Fermi surface symmetry breaking and superconductivity

TL;DR

This paper investigates how competing interactions in a square lattice model lead to complex phase diagrams, including coexistence and suppression of Fermi surface symmetry breaking and d-wave superconductivity, revealing quantum critical points.

Contribution

It introduces a mean-field model capturing the interplay between Fermi surface symmetry breaking and superconductivity, highlighting conditions for coexistence and phase transition nature.

Findings

Fermi surface symmetry breaking coexists with superconductivity near van Hove filling.

Superconductivity can suppress or limit Fermi surface symmetry breaking at various temperatures.

Presence of superconductivity can change the order of phase transitions, creating quantum critical points.

Abstract

We analyze a mean-field model of electrons on a square lattice with two types of interaction: forward scattering favoring a d-wave Pomeranchuk instability and a BCS pairing interaction driving d-wave superconductivity. Tuning the interaction parameters a rich variety of phase diagrams is obtained. If the BCS interaction is not too strong, Fermi surface symmetry breaking is stabilized around van Hove filling, and coexists with superconductivity at low temperatures. For pure forward scattering Fermi surface symmetry breaking occurs typically via a first order transition at low temperatures. The presence of superconductivity reduces the first order character of this transition and, if strong enough, can turn it into a continuous one. This gives rise to a quantum critical point within the superconducting phase. The superconducting gap tends to suppress Fermi surface symmetry breaking. For a relatively strong BCS interaction, Fermi surface symmetry breaking can be limited to intermediate temperatures, or can be suppressed completely by pairing.