Impact of Superconductors’ Properties on the Measurement Sensitivity of Resonant-Based Axion Detectors

Axions, hypothetical particles theorised to solve the strong CP problem, are presently being considered as strong candidates for cold dark matter constituents. The signal power of resonant-based axion detectors, known as haloscopes, is directly proportional to their quality factor Q. In this paper, the impact of the use of superconductors on the performances of haloscopes is studied by evaluating the obtainable Q. In particular, the surface resistance Rs of NbTi, Nb3Sn, YBa2Cu3O7−δ, and FeSe0.5Te0.5 is computed in the frequency, magnetic field, and temperature ranges of interest, starting from the measured vortex motion complex resistivity and the screening lengths of these materials. From Rs, the quality factor Q of a cylindrical haloscope with copper conical bases and a superconductive lateral wall, operating with the TM010 mode, is evaluated and used to perform a comparison of the performances of the different materials. Both YBa2Cu3O7−δ and FeSe0.5Te0.5 are shown to improve the measurement sensitivity by almost an order of magnitude, with respect to a whole Cu cavity, while NbTi is shown to be suitable only at lower frequencies (<10 GHz). Nb3Sn can provide an intermediate improvement of the whole spectrum of interest.