Emitted spectra of electromagnetic waves from a tunnel-injected nonequilibrium high-T-c YBa2Cu3O7-y superconductor

We report the measurements on the emitted spectra of terahertz electromagnetic waves from a tunnel-injected nonequilibrium high-T-c YBa2Cu3O7-y (YBCO) superconductor using a high-T-c YBCO Josephson spectroscopic detector fabricated on the same chip. The observed spectrum appeared as a single broad-peaked structure with peak frequency typically at about 5 THz at low temperature. The dependencies of peak frequency and line shape on temperature, c-axis current, and oxygen deficiency are investigated. The results are consistently interpreted in terms of Josephson plasma emission characteristic of oxide sugerconductors with optimal doping.