terahertz sources*

The extremely anisotropic high-temperature superconductor Bi₂Sr₂CaCu₂O₈ contains stacked 'intrinsic' Josephson junctions with a large superconducting gap energy. Mesa-shaped devices constructed from this material therefore show promise as a source of coherent, continuous-wave radiation in the 'terahertz gap' range.

THz emission from these devices has previously been typically observed at frequencies between around 0.4 THz – 2 THz, corresponding to Josephson voltages of between 0.8 mV and 4 mV per intrinsic junction. However, we have recently observed a new mode of emission which occurs at bias currents below the retrapping current of the stacked Josephson junctions. The maximum emitted THz power that can be generated from this mode is comparable to that generated by the more well-established and better-understood THz emission modes in Bi₂Sr₂CaCu₂O₈ mesa sources. We will discuss the most likely mechanism for this emission mode, which can most probably be ascribed to the stacked intrinsic Josephson junctions acting as an antenna for other current-biased junctions located in the Bi₂Sr₂CaCu₂O₈ base crystal of the device. We will also discuss possible future directions of related research.