Pairing gaps near ferromagnetic quantum critical points

TL;DR

This paper investigates the quantum-critical behavior of two-dimensional itinerant ferromagnetic systems, analyzing how fluctuations affect superconducting order near critical points across different magnetic models.

Contribution

It provides a detailed analysis of fluctuation effects on superconducting order in various ferromagnetic and nematic quantum critical systems using a nonlinear sigma model.

Findings

Superconducting quasi-long-range order persists in Ising-like models.

Long-range order is destroyed in Heisenberg ferromagnets due to fluctuations.

Fluctuations are not suppressed by small parameters, impacting order stability.

Abstract

We address the quantum-critical behavior of a two-dimensional itinerant ferromagnetic systems described by a spin-fermion model in which fermions interact with close to critical bosonic modes. We consider Heisenberg ferromagnets, Ising ferromagnets, and the Ising nematic transition. Mean-field theory close to the quantum critical point predicts a superconducting gap with spin-triplet symmetry for the ferromagnetic systems and a singlet gap for the nematic scenario. Studying fluctuations in this ordered phase using a nonlinear sigma model, we find that these fluctuations are not suppressed by any small parameter. As a result, we find that a superconducting quasi-long-range order is still possible in the Ising-like models but long-range order is destroyed in Heisenberg ferromagnets.