Impact of the superconductors properties on the measurement sensitivity of resonant-based axion detectors

Abstract

Axions, hypothetical particles theorized to solve the strong CP-problem, are presently being considered as strong candidates as 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 in the performances of the haloscopes is studied by evaluating the obtainable $Q$. In particular, the surface resistance $R_s$ of NbTi, Nb$_3$Sn, YBa$_2$Cu$_3$O$_{7-\delta}$ and FeSe$_{0.5}$Te$_{0.5}$ is computed in the frequency, magnetic field and temperature ranges of interest, starting from the measured vortex motion complex resistivity and screening lengths of these materials. From $R_s$ the quality factor $Q$ of a cylindrical haloscope with copper conical bases and superconductive lateral wall, operating with the TM$_{010}$ mode, is evaluated and used to perform a comparison of the performances of the different materials. Both YBa$_2$Cu$_3$O$_{7-\delta}$ and FeSe$_{0.5}$Te$_{0.5}$ 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). Nb$_3$Sn can give an intermediate improvement in the whole spectrum of interest.