Stable Higgs mode in anisotropic quantum magnets

TL;DR

This paper demonstrates that easy axis anisotropy in quantum magnets near a quantum critical point stabilizes the Higgs mode by preventing its decay into magnons, making it observable in condensed matter systems.

Contribution

It reveals that anisotropic quantum magnets can host a stable Higgs mode near the quantum critical point, providing a new platform for exploring Higgs physics in condensed matter.

Findings

A stable Higgs mode exists near the quantum critical point in anisotropic quantum magnets.

Easy axis anisotropy increases the magnon gap, preventing Higgs decay.

The results suggest anisotropic quantum magnets as ideal platforms for Higgs physics.

Abstract

Low-energy excitations associated with the amplitude fluctuation of an order parameter in condensed matter systems can mimic the Higgs boson, an elementary particle in the standard model, and are dubbed as Higgs modes. Identifying the condensed-matter Higgs mode is challenging because it is known in many cases to decay rapidly into other low-energy bosonic modes, which renders the Higgs mode invisible. Therefore, it is desirable to find a way to stabilize the Higgs mode, which can offer an insight into the stabilization mechanism of the Higgs mode in condensed matter physics. In quantum magnets, magnetic order caused by spontaneous symmetry breaking supports transverse (magnons) and longitudinal (Higgs modes) fluctuations. When a continuous symmetry is broken, the Goldstone magnon mode generally has a lower excitation energy than the Higgs mode, causing a rapid decay of the latter. In this work, we show that a stable Higgs mode exists in anisotropic quantum magnets near the quantum critical point between the dimerized and magnetically ordered phases. We find that an easy axis anisotropy increases the magnon gap such that the magnon mode is above the Higgs mode near the quantum critical point, and the decay of the Higgs mode into the magnon mode is forbidden kinematically. Our results suggest that the anisotropic quantum magnets provide ideal platforms to explore the Higgs physics in condensed matter systems.