Linewidth Dependence of Coherent Terahertz Waves Emitted from a Stack of Intrinsic Josephson Junctions in BSCCO

The observation of coherent terahertz radiation from a stack of intrinsic Josephson junctions in BSCCO [L. Ozyuzer et al., Science (2007)] highlighted the possibility of using high-transition-temperature superconductors (HTS) as a novel terahertz source. The coherence of the emitted waves from HTS was investigated by linewidth measurements using a superconducting integrated receiver [M. Li, et al., PRB (2012)]. A peculiar line shape with relatively narrower linewidth down to 23 MHz was observed in the high-bias regimes, where temperature distribution in the emitting stack is extremely inhomogeneous. Here, we present a new measurement system based on the heterodyne technique using a sub-harmonic diode mixer. In order to unveil the intrinsic behavior of linewidths independently of the temperature inhomogeneity in the stack, we measured the line shapes associated with the terahertz waves emitted from stand-alone-type mesa samples that form rather uniform temperature distributions due to better cooling. In this talk, we will present experimental results related to the linewidth measurements.