Experimental validation of a microstrip antenna model for high-T c superconducting terahertz emitters

Abstract

We experimentally verified a proposed microstrip antenna model for high-$T_c$ superconducting coherent terahertz emitters. We attached conductive metal patches to single crystalline Bi${}_2$ Sr${}_2$ CuCu${}_2$ O${}_{8+\delta }$ mesas to probe the electromagnetic resonance conditions near the mesa sidewalls, where the coherent terahertz radiation is emitted. A systematic experiment reveals that an internal cavity resonance, which is an essential ingredient for outside radiation, remains unaltered by the presence of the ambient microstrip patterns. We found that an emission frequency is well predicted by the proposed model and that, in contrast to the conventional microstrip antenna, the internal cavity mode is more robust to the external microstrip patterns than expected from the proposed model. The experimental result requires us to modify the model to allow for a spontaneous synchronization of intrinsic Josephson oscillations that stimulates the stable excitation of the internal cavity resonance.