Axion detection with phonon-polaritons revisited

TL;DR

This paper revisits axion detection via phonon-polaritons, incorporating finite volume effects and material losses, and suggests that low-loss materials at cryogenic temperatures could enable probing QCD axions around 100 meV.

Contribution

It provides a revised calculation of axion-photon conversion power considering realistic material properties and boundary effects, guiding future experimental searches.

Findings

Lower signal magnitude than previous estimates.

Resonance features in dielectric functions can optimize sensitivity.

Potential to detect QCD axions around 100 meV with improved detectors.

Abstract

In the presence of a background magnetic field, axion dark matter induces an electric field and can thus excite phonon-polaritons in suitable materials. We revisit the calculation of the axion-photon conversion power output from such materials, accounting for finite volume effects, and material losses. Our calculation shows how phonon-polaritons can be converted to propagating photons at the material boundary, offering a route to detecting the signal. Using the dielectric functions of GaAs, Al$_2$O$_3$, and SiO$_2$, a fit to our loss model leads to a signal of lower magnitude than previous calculations. We demonstrate how knowledge of resonances in the dielectric function can directly be used to calculate the sensitivity of any material to axion dark matter. We argue that a combination of low losses encountered at $\mathcal{O}(1)$ K temperatures and near future improvements in detector dark count allow one to probe the QCD axion in the mass range $m_a\approx 100$ meV. This provides further impetus to examine novel materials and further develop detectors in the THz regime. We also discuss possible tuning methods to scan the axion mass.