The 'Higgs' amplitude mode in weak ferromagnetic metals

TL;DR

This paper identifies a Higgs amplitude mode in weak ferromagnetic metals, specifically in MnSi, using Fermi liquid theory, and suggests it can be observed via neutron scattering.

Contribution

It introduces the Higgs amplitude mode in weak ferromagnetic metals and demonstrates its detectability in MnSi through theoretical modeling and experimental data fitting.

Findings

The Higgs mode appears as a distinct peak in the dynamical structure function.

The model's predictions align with existing experimental results.

The Higgs mode's intensity suggests it is observable in neutron scattering experiments.

Abstract

Using Ferromagnetic Fermi liquid theory, Bedell and Blagoev derived the collective low-energy excitations of a weak ferromagnet. They obtained the well-known magnon (Nambu-Goldstone) mode and found a new gapped mode that was never studied in weak ferromagnetic metals. In this article we have identified this mode as the Higgs boson (amplitude mode) of a ferromagnetic metal. This is identified as the Higgs since it can be show that it corresponds to a fluctuation of the amplitude of the order parameter. We use this model to describe the itinerant-electron ferromagnetic material MnSi. By fitting the model with the existing experimental results, we calculate the dynamical structure function and see well-defined peaks contributed from the magnon and the Higgs. Our estimates of the relative intensity of the Higgs amplitude mode suggest that it can be seen in neutron scattering experiments on MnSi.