Optimal anti-ferromagnets for light dark matter detection

TL;DR

This paper suggests anti-ferromagnetic materials, especially nickel oxide, as highly effective targets for detecting light dark matter particles through multi-magnon emission, enabling sensitivity to keV-scale dark matter.

Contribution

It introduces anti-ferromagnets as optimal detection targets for light dark matter and provides a theoretical framework to estimate event rates.

Findings

Nickel oxide identified as an ideal target material.

Anti-ferromagnets enable detection of dark matter as light as keV.

Multi-magnon emission enhances sensitivity to small momentum transfers.

Abstract

We propose anti-ferromagnets as optimal targets to hunt for sub-MeV dark matter with spin-dependent interactions. These materials allow for multi-magnon emission even for very small momentum transfers, and are therefore sensitive to dark matter particles as light as the keV. We use an effective theory to compute the event rates in a simple way. Among the materials studied here, we identify nickel oxide (a well-assessed anti-ferromagnet) as an ideal candidate target. Indeed, the propagation speed of its gapless magnons is very close to the typical dark matter velocity, allowing the absorption of all its kinetic energy, even through the emission of just a single magnon.