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 E_J of the device. We demonstrate current-gain enhancement for the device operating near the bifurcation point at small E_J. From our results for the current gains at various E_J, we determine the bifurcation threshold on the E_J-base current plane. The bifurcation threshold curve can be understood using the interplay of interband and intraband tunneling events.