Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge m0 = ±(h/ μ0e) and quantized magnetic flux φ0= ±h/e. A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux φ threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theoretical discovery that a plasma containing equal numbers of emergent magnetic charges ±m* should exist in several lanthanide-pyrochlore magnetic insulators including Dy2Ti2O7, this SQUID technique was proposed for their direct detection. 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 spontaneously generated magnetic-flux noise Sφ(ω, T) due to a thermally generated plasma of magnetic monopoles ±m* to be predicted for Dy2Ti2O7. I will describe development of a high-sensitivity, SQUID based flux-noise spectrometer, and consequent measurements of the frequency and temperature dependence of Sφ(ω, T) for Dy2Ti2O7 samples. Virtually all the elements of Sφ(ω, T) predicted for a magnetic monopole plasma, including the existence of intense magnetization noise and its characteristic frequency and temperature dependence, are detected directly. Moreover, measured correlation functions Cφ(t) of the magnetic-flux noise φ(t) reveal that the motion of magnetic charges is correlated. A final striking observation is that, since the GR time constants τ(T) are in the millisecond range for Dy2Ti2O7, magnetic monopole flux noise amplified by the SQUID is audible to human perception.
Ritika Dusad received her B.S. in Physics from University of California, Los Angles in 2012. She is currently a PhD student in the Laboratory of Atomic and Solid State Physics at Cornell University, conducting her research under the guidance of Prof. Seamus Davis. Her current research interests are in devising innovative experiments to detect spin liquids and chirality transfer in topological materials.