  An atomtronic transistor circuit is used to realize a driven matterwave
oscillator. The transistor consists of Source and Drain regions separated by a
narrow Gate well. Quasi-steady-state behavior is determined from a
thermodynamic model, which reveals two oscillation threshold regimes. One is
due to the onset of Bose-Einstein condensation in the Gate well, the other is
due to the appearance of a negative transresistance regime of the transistor.
The thresholds of oscillation are shown to be primarily dependent on the
potential energy height difference between Gate-Drain and Gate-Source barriers.
The transistor potential is established with a combination of magnetic and
optical fields using a compound glass and silicon substrate atom chip. The
onset of oscillation and the output matterwave are observed through in-trap
imaging. Time-of-flight absorption imaging is used to determine the time
dependence of the Source well thermal and chemical energies as well as to
estimate the value of the closed-loop ohmic Gate resistance, which is negative
and is observed to cause cooling of Source atoms.
