Dynamics of Bloch oscillating transistor near the bifurcation threshold

The tendency to bifurcate can often be utilized to improve performance characteristics of amplifiers or even to build detectors. The Bloch oscillating transistor is such a device. Here, we show that bistable behavior can be approached by tuning the base current and that the critical value depends on the Josephson coupling energy EJ of the device. We demonstrate current-gain enhancement for the device operating near the bifurcation point at small EJ. From our results for the current gains at various EJ, we determine the bifurcation threshold on the EJ-base current plane. The bifurcation threshold curve can be understood using the interplay of interband and intraband tunneling events