University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Friday, April 19th 2019
11:00 am:
Speaker: Ritika Dusad, Cornell University
Subject: Magnetic Monopole Noise

Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge m_0=±(h⁄(μ_0 e)) and quantized magnetic flux ϕ_0=±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 Dy_2Ti_2O_7, 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 S_Φ (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 S_Φ (ω,T) for Dy2Ti2O7 samples. Virtually all the elements of S_Φ (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 C_Φ (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.

Faculty Host: Vlad Pribiag

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