J.C. Séamus Davis

Magnetic Monopole Noise

Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge  and quantized magnetic flux . A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux  threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theoretical discovery that a plasma of emergent magnetic charges should exist in several lanthanide-pyrochlore magnetic insulators including Dy₂Ti₂O_7, this SQUID technique was proposed for their direct detection (Nature 451, 42 (2008)). Experimentally, this has proven extremely challenging because of the high number density, and the generation-recombination (GR) fluctuations, of the monopole plasma. Recently, however, theoretical advances have allowed the­ spectral density of magnetic-flux noise  due to GR fluctuations of magnetic charge pairs to be determined. In response, we developed a high-sensitivity, SQUID based flux-noise spectrometer, and used this new instrument to measure the frequency and temperature dependence of  for Dy₂Ti₂O₇ samples, and discovered the magnetic noise generated by a fluid of monopoles. R. Dusad et al Nature (2019) and https://arxiv.1901.10044.