Field-induced magnon decays in dipolar quantum magnets

TL;DR

This paper explores how long-range dipolar interactions influence magnon decay processes in two-dimensional quantum magnets, revealing unique decay behaviors and spectral singularities that differ from short-range interaction systems.

Contribution

It demonstrates that dipolar interactions significantly alter magnon decay conditions, introducing decay in staggered fields without a threshold and predicting spectral singularities due to topological transitions.

Findings

Magnons do not decay in uniform fields due to dispersion constraints.

Decays occur in staggered fields without a minimum threshold.

Spectral singularities arise from topological transitions in decay surfaces.

Abstract

We investigate the spontaneous disintegration of magnons in two-dimensional ferromagnets and antiferromagnets dominated by long-range dipolar interactions. Analyzing kinematic constraints, we show that the unusual dispersion of dipolar ferromagnets in a uniform magnetic field precludes magnon-decay at all fields, in sharp contrast to short-range exchange-driven magnets. However, in a staggered magnetic field, magnons can decay in both dipolar ferromagnets and antiferromagnets. Remarkably, such decays do not require a minimum threshold field, and happen over a nearly fixed fraction of the Brillouin Zone in the XY limit, highlighting the significant role played by dipolar interactions. In addition, topological transitions in the decay surfaces lead to singularities in the magnon spectrum. Regularizing such singular behavior via a self-consistent approach, we make predictions for dynamical spin correlations accessible to near-term quantum simulators and sensors.