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.
Highlights
The QCD axion [1,2,3,4] remains one of the best-motivated and predictive models of dark matter (DM) [5,6,7]
Many more experiments plan to join this search. These include the magnetized disk and mirror axion experiment [15,16], which uses a layered dielectric in an external magnetic field, and the quaere axion (QUAX) experiment [17,18,19], which searches for axion-induced classical spin waves inside a magnetic target
For DM coupling to the effective spins Slj, the interaction is given by Eq (4), and we find, in complete analogy with Eq (16), δH 0j0i
Summary
The QCD axion [1,2,3,4] remains one of the best-motivated and predictive models of dark matter (DM) [5,6,7]. The use of axionic topological antiferromagnets has been proposed to detect axions in this region [48], such materials have not been fabricated yet in the lab, and even this proposal is limited to ma ≲ 10 meV Rate estimate(on resonance) g2aγγ ρa ZÃ2e2B2 m3a ε2∞m2ionγ [Eq. spin, gaee, allows for magnon excitation, while the axioninduced electric field in the presence of an external magnetic field, due to the axion-photon coupling gaγγ, can excite phonon polaritons. Spin, gaee, allows for magnon excitation, while the axioninduced electric field in the presence of an external magnetic field, due to the axion-photon coupling gaγγ, can excite phonon polaritons VI and discuss future interdisciplinary work needed to better understand and realize the potential of the ideas presented in this work
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