Frequency characterization of individual open-ring resonators by terahertz Josephson spectroscopy

Excitation of various resonance modes in a square open-loop resonator was studied by Josephson spectroscopy. A copper resonator with a side of a square of 233 μm was fabricated. Changing the position of the resonator with respect to a bicrystal YBa 2 Cu 3 O 7−x Josephson junction, a number of resonances was observed in measured spectra with the center frequencies from 78 GHz to 218 GHz. Measured data were compared with the results of a numeric simulation using an equivalent circuit of the resonator interacting with the junction. Resonance frequencies were obtained by fitting of calculated characteristics to the measured ones. According to the geometry of electric and magnetic field distributions for each position of the resonator, resonances observed were ascribed to excitation of fundamental magnetic and plasmonic modes.