Topological Circulators and their implementation in Axion Haloscopes

Recent microwave cavity experiments have made significant progress in achieving the required sensitivity to detect axions of a few micro-eV mass, or around a GHz in frequency. However, searches for axions of higher masses are challenging because the experimental sensitivity drops dramatically as cavity volumes decrease to realize higher resonant frequencies. To achieve the sensitivity necessary to search for high-mass axions, new microwave technologies must be developed that scale up the detection volume, enhance the transmission efficiency between the amplifier and the cavity, and reduce the heat load from the components used to read out the cavity. Here we demonstrate a low-loss, small foot-print topological circulator that can work at a wide range of magnetic fields. Topology enables magnetic topological insulators to support robust chiral edge currents that flow either clockwise or counterclockwise around the boundary of the sample without resistance. This property will greatly facilitate the operation of an Axion Haloscope and other HEP detectors that may require cryogenic RF routing near high magnetic fields.