Speaker
Description
Single crystal calcium tungstate (CaWO_4) is an important crystal for WIMP dark matter searches and more recently has become an interesting material for microwave quantum electrodynamic experiments that investigate spins in solids. We construct a dielectrically loaded microwave cavity resonator from a cylindrical single crystal of CaWO_4 and perform whispering gallery multi-mode spectroscopy at 30mK in temperature. This study found many high-Q modes of up to O(10^7) in value indicating a low dielectric loss tangent of order O(10^−7). The low-loss at low temperatures enables high sensitivity analysis of photon-spin interactions while the use of multiple high-Q modes allows the measurements of spin g-factors and zero field splittings, allowing identification and characterization of spins. In our sample, spin concentrations of O(10^13) cm^−3 were derived from spectroscopic analysis of the crystal. The presence of Gd3+ impurity has been implicated along with other as yet unidentified transition metals.
