Light stable axions, originally proposed to solve the strong CP problem of quantum chromodynamics (QCD), emerge as leading candidates of non-WIMP dark matter. They are produced non-thermally in the early universe, and now result in a coherently oscillating sea of pseudo-scalar field particles that fills the dark matter halos of galaxies. The associated phenomenology can be described as a modification of Maxwell equations that can be investigated in laboratory experiments. Dark matter axions are intensively searched in experiments mostly based on resonant axion-photon conversion in a static magnetic field via Primakoff effect, as in the ADMX haloscope. However, the axion-electron coupling, explicitly predicted by some models, can be exploited to envisage novel classes of haloscopes, allowing for the discrimination among axion models in case of detection.
In this talk we discuss tabletop-scale experiments in axion detection, particularly focusing on new observables for direct detection of axionic dark matter, and on the ongoing experimental activity at LNL.
In particular, in the QUAX experiment we propose to measure the magnetization changes induced by axion interactions with electrons in a ferrimagnetic sample, while in the AXIOMA experiment we study the possibility to detect atomic transitions from the ground level to the upper Zeeman level of rare earth atoms in suitable rare-earth doped crystalline matrices. The experimental parameters required to achieve cosmologically relevant sensitivity in both approaches will be discussed.