Electromagnetic properties of terbium gallium garnet at millikelvin temperatures and single photon energy

摘要

Electromagnetic properties of single crystal terbium gallium garnet (TGG) arecharacterised from room down to millikelvin temperatures using the whisperinggallery mode method. Microwave spectroscopy is performed at low powersequivalent to a few photons in energy and conducted as functions of themagnetic field and temperature. A phase transition is detected close to thetemperature of 3.5 K. This is observed for multiple whispering gallery modescausing an abrupt negative frequency shift and a change in transmission due toextra losses in the new phase caused by a change in complex magneticsusceptibility.