Principal Investigator Karl Berggren
Superconductors are ideal platforms for studying non- linear behavior due to their nonlinear switching dynamics and phase relationships. Josephson junctions (JJs), the most common superconducting devices, have a nonlinear current-phase relationship that allows them to phase lock to weak external periodic drives. This phenomenon, known as the AC Josephson effect, produces distinct DC steps in the time-averaged cur- rent-voltage characteristics at voltage intervals of Vn = nhf/2e, where n is an integer, h is Planck’s constant, f is the frequency of the external radiation, and e is the electronic charge. Such a relationship has enabled technology such as the Josephson voltage standard and analog-to-digital converters.Unlike JJs, superconducting nanowires are governed by a thermal nonlinearity that controls the switching into and out of the resistive state. In this work,
we have studied fast oscillations in superconducting nanowires based on the electrothermal feedback between the nanowire hotspot and an external shunt resistor with a series inductance. In addition to studying how circuit parameters influence the frequency of the oscillations, we show that the oscillations can mix with an external microwave drive and eventually phase lock. This process produces a nanowire analog to the AC Josephson effect, with steps occurring at intervals of Vn = nfIcL, here n is an integer, f is the frequency of the drive, Ic is the critical current of the nanowire, and L is the series inductance. In addition to offering a potential avenue for measuring inductance through the appearance of phase-locked steps, the ability of these oscillations to mix with an external drive is promising for applications such as parametric amplification and frequency multiplexing.