Detectability of Axion Dark Matter with Phonon Polaritons and Magnons

TL;DR

This paper proposes using collective excitations like phonons and magnons in condensed matter systems as novel methods to detect QCD axion dark matter within a specific mass range, leveraging axion-induced excitations in polar and magnetic materials.

Contribution

It introduces a new detection approach for axion dark matter using phonon polaritons and magnons, identifying material requirements and outlining experimental strategies.

Findings

Detection of axion-induced phonon polaritons and magnons is feasible with kilogram-year exposure.

Materials with multiple resonant modes can enhance axion detection sensitivity.

Development of single photon, phonon, and magnon detectors is crucial for experimental realization.

Abstract

Collective excitations in condensed matter systems, such as phonons and magnons, have recently been proposed as novel detection channels for light dark matter. We show that excitation of i) optical phonon polaritons in polar materials in an ${\mathcal O}$(1 T) magnetic field (via the axion-photon coupling), and ii) gapped magnons in magnetically ordered materials (via the axion wind coupling to the electron spin), can cover the difficult-to-reach ${\mathcal O}$(1-100) meV mass window of QCD axion dark matter with less than a kilogram-year exposure. Finding materials with a large number of optical phonon or magnon modes that can couple to the axion field is crucial, suggesting a program to search for a range of materials with different resonant energies and excitation selection rules; we outline the rules and discuss a few candidate targets, leaving a more exhaustive search for future work. Ongoing development of single photon, phonon and magnon detectors will provide the key for experimentally realizing the ideas presented here.