Spontaneous magnon decay in two-dimensional altermagnets

TL;DR

This paper demonstrates that in two-dimensional altermagnets, magnons can spontaneously decay at zero temperature due to quantum fluctuations, with decay rates depending on wavevector and magnon chirality, revealing new decay mechanisms.

Contribution

It reveals the phenomenon of spontaneous magnon decay in 2D altermagnets and characterizes the decay rate's dependence on wavevector and chirality, a novel insight in magnetic excitations.

Findings

Magnons in 2D altermagnets can decay at zero temperature.

Decay rate scales as $k^5$ for small wavevectors with directional dependence.

Only magnons of specific chirality can decay at a given momentum.

Abstract

We show that magnons in two-dimensional altermagnets can spontaneously decay at zero temperature. The decay rate is determined by quantum fluctuations and scattering processes involving the decay of a single magnon into three. These processes are kinematically allowed due to the convexity of the altermagnetic magnon dispersion. For small wavevectors $k$ the decay rate is proportional to $k^5$ with a direction-dependent prefactor which is maximal along the diagonals of the Brillouin zone. Moreover, for a given momentum only magnons with one specific chirality can spontaneously decay.