Broadening frequency range of a ferromagnetic axion haloscope with strongly coupled cavity–magnon polaritons

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With the axion being a prime candidate for dark matter, there has been some recent interest in direct detection through a so called ‘Ferromagnetic haloscope.’ Such devices exploit the coupling between axions and electrons in the form of collective spin excitations of magnetic materials with the readout through a microwave cavity. Here, we present a new, general, theoretical treatment of such experiments in a Hamiltonian formulation for strongly coupled magnons and photons, which hybridise as cavity–magnon polaritons. Such strongly coupled systems have an extended measurable dispersive regime. Thus, we extend the analysis and operation of such experiments into the dispersive regime, which allows any ferromagnetic haloscope to achieve improved bandwidth with respect to the axion mass parameter space. This experiment was implemented in a cryogenic setup, and initial search results are presented setting laboratory limits on the axion–electron coupling strength of gaee>3.7×10−9 in the range 33.79μeV<ma<33.94μeV with 95% confidence. The potential bandwidth of the Ferromagnetic haloscope was calculated to be in two bands, the first of about 1 GHz around 8.24 GHz (or 4.1μeV mass range around 34.1μeV) and the second of about 1.6 GHz around 10 GHz (6.6μeV mass range around 41.4μeV). Frequency tuning may also be easily achieved via an external magnetic field which changes the ferromagnetic resonant frequency with respect to the cavity frequency. The requirements necessary for future improvements to reach the DFSZ axion model band are discussed in the paper.

Original languageEnglish
Article number100306
JournalPhysics Of The Dark Universe
Publication statusPublished - 1 Sept 2019


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