ADMX SLIC: Results from a Superconducting LC Circuit Investigating Cold Axions

Axions are a promising cold dark matter candidate. Haloscopes, which use the conversion of axions to photons in the presence of a magnetic field to detect axions, are the basis of microwave cavity searches such as the Axion Dark Matter eXperiment (ADMX). To search for lighter, low frequency axions in the sub- $2\times {10}^{-7}\mathrm{eV}$ (50 MHz) range, a tunable lumped-element LC circuit has been proposed. For the first time, through ADMX SLIC (Superconducting LC Circuit Investigating Cold Axions), a resonant LC circuit was used to probe this region of axion mass-coupling space. The detector used a superconducting LC circuit with piezoelectric driven capacitive tuning. The axion mass and corresponding frequency ranges $1.7498–1.7519\times {10}^{-7}\mathrm{eV}$ (42.31–42.36 MHz), $1.7734–1.7738\times {10}^{-7}\mathrm{eV}$ (42.88–42.89 MHz), and $1.8007–1.8015\times {10}^{-7}\mathrm{eV}$ (43.54–43.56 MHz) were covered at magnetic fields of 4.5 T, 5.0 T, and 7.0 T, respectively. Exclusion results from the search data, for coupling below ${10}^{-12}{\mathrm{GeV}}^{-1}$, are presented.

Figure 1

A sketch of the experiment layout of ADMX SLIC. Two additional weakly coupled probes, for $S_{21}$ measurements and an optional amplifier bypass, are not shown.

Figure 2

Receiver chain diagram of ADMX SLIC.

Figure 3

$S_{21}$ measurements of the loop antenna taken over the course of a magnet ramp. A frequency shift and $Q$ reduction track the increased magnetic field.

Figure 4

Individual and combined limits collected by ADMX SLIC.