Abstract
Josephson junctions with weak-links of exotic materials allow the elucidation of the Josephson effect in previously unexplored regimes. Further, such devices offer a direct probe of novel material properties, for example in the search for Majorana fermions. In this work, we report on DC and AC Josephson effect of high-mobility, hexagonal boron nitride (h-BN) encapsulated graphene Josephson junctions. On the application of RF radiation, we measure phase-locked Shapiro steps. An unexpected bistability between $\pm 1$ steps is observed with switching times on the order of seconds. A critical scaling of a bistable state is measured directly from the switching time, allowing for direct comparison to numerical simulations. We show such intermittent chaotic behavior is a consequence of the nonlinear dynamics of the junction and has a sensitive dependence on the current-phase relation. This work draws connections between nonlinear phenomena in dynamical systems and their implications for ongoing condensed matter experiments exploring topology and exotic physics.
Highlights
The ground-state wave function of a superconductor is endowed with an emergent phase on the macroscopic scale [1]
In order to probe the phase dynamics of the Josephson junction (JJ), R is measured as a function of Idc and rf power
Having understood the origin of bistability in simulation, we focus on the changes in switching time τ as a function of dc and ac currents
Summary
The ground-state wave function of a superconductor is endowed with an emergent phase on the macroscopic scale [1]. The ac Josephson effect has been proposed as a means to detect topological superconductivity, where the 4π -periodic CPR results in a doubling of the Shapiro step height [7,8,9] While this is an effective and reliable signature for overdamped JJs, nonlinear effects in moderately and heavily damped junctions can produce a period doubling bifurcation [24], which would emulate the effects expected in a topological JJ. The timescale is shown to depend sensitively on the CPR of the junction, becoming large for skewed CPRs like that predicted for weak link materials possessing a Dirac (linear) energy dispersion These results should inform future experiments using rf radiation to probe exotic materials in JJs [7,8,9] and devices that exploit JJs in rf environments [25,26]
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