Research Status 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 fluid of emergent magnetic charges should exist in several lanthanide-pyrochlore magnetic insulators including Dy_{2}Ti_{2}O_{7}, this SQUID technique was proposed for their direct detection (Castelnovo et. al. Nature 451, 42 (2008)). Experimentally, this has proven extremely challenging because of the high number density, and generation-recombination (GR) fluctuations, of the monopole plasma. Recently, however, theoretical advances by Prof. S. Blundell of Oxford University have allowed the spectral density of spin-noise S_{Φ}(ω,T) due to GR fluctuations of ±m^{*} magnetic charge pairs to be determined. Fig. 2A The sequence of Dy spin flips in Dy_{2}Ti_{2}O_{7} that generate two magnetic monopoles of opposite charge propagating through the material. B) When these monopoles are created within the input coil of a DC SQUID and depart to infinity in opposite directions, the flux through the SQUID jumps by Φ =m^{*}μ_{0}. In 2018 we developed a high-sensitivity, SQUID based spin-noise spectrometer, and measured the frequency and temperature dependence of S_{Φ}(ω,T) for Dy_{2}Ti_{2}O_{7} samples. Virtually all the elements of S_{Φ}(ω,T) predicted for a magnetic monopole fluid, including the existence of intense magnetization noise and its characteristic frequency and temperature dependence, are detected. This provides the first direct access to the microscopic physics a monopole fluid. |
Research Plans High precision measurement of the spin-noise spectrum is an innovative approach to magnetic quantum fluids. It opens a wide variety of new research avenues including the following projects of immediate interest: |
Collaborators |