Speaker
Description
Dark matter axions can generate peculiar effects in special types of Josephson junctions, so-called SNS junctions [1]. One can show that the axion field equations in a Josephson environment allow for very small oscillating supercurrents, which manifest themselves as a tiny wiggle in the I-V curve, a so-called Shapiro step, which occurs at a frequency given by the axion mass. The effect is very small but perfectly measurable in modern nanotechnological devices. In this talk I will summarize the theory and then present evidence that candidate Shapiro steps of this type have indeed been seen in several independent experiments [2]. Assuming the observed tiny Shapiro steps are due to axion flow then these data consistently point to an axion mass of about 110 $\mu$eV, consistent with what is expected for the QCD axion. In addition to the above small Shapiro resonance effects at frequencies in the GHz region one also expects to see broad-band noise effects at much lower frequencies [3]. Overall this approach provides a novel pathway for the future design of new types of axionic dark matter detectors.
[1] C. Beck, Possible resonance effect of axionic dark matter in Josephson junctions, Phys. Rev. Lett. 111, 231801 (2013)
[2] C. Beck, Axion mass estimates from resonant Josephson junctions, Phys. Dark Univ. 7-8, 6-11 (2015)
[3] C. Beck, Cosmological flux noise and measured noise power spectra in SQUIDs,
Scient. Rep. 6, 28275 (2016)
