Hidden Quantum Critical Point in a Ferromagnetic Superconductor

TL;DR

This paper investigates the coexistence of ferromagnetism and superconductivity, revealing a hidden quantum critical point where the superconducting gap vanishes but magnetization persists, with notable effects on effective mass and spin wave stiffness.

Contribution

It demonstrates that the superconducting gap closes at the Stoner point while magnetization remains finite, indicating a hidden quantum critical point in ferromagnetic superconductors.

Findings

Superconducting gap vanishes at the Stoner point.

Magnetization remains finite at the quantum critical point.

Effective mass is enhanced near the critical point.

Abstract

We consider a coexistence phase of both Ferromagnetism and superconductivity and solve the self-consistent mean-field equations at zero temperature. The superconducting gap is shown to vanish at the Stoner point whereas the magnetization doesn't. This indicates that the para-Ferro quantum critical point becomes a hidden critical point. The effective mass in such a phase gets enhanced whereas the spin wave stiffness is reduced as compared to the pure FM phase. The spin wave stiffness remains finite even at the para-Ferro quantum critical point.