The Multi-terminal Inverse AC Josephson Effect

TL;DR

This paper investigates the inverse AC Josephson effect in a multi-terminal graphene-based superconducting device, revealing fractional Shapiro steps and complex network behaviors, supported by experimental observations and simulations.

Contribution

It introduces the study of multi-terminal Josephson junctions with three or more contacts, demonstrating complex phase dynamics and fractional Shapiro steps not seen in simpler junctions.

Findings

Observation of robust fractional Shapiro steps

Correlated switching events in the junction network

Successful simulation with a modified 2D RCSJ model

Abstract

When a Josephson junction is exposed to microwave radiation, it undergoes the inverse AC Josephson effect - the phase of the junction locks to the drive frequency. As a result, the I-V curves of the junction acquire "Shapiro steps" of quantized voltage. If the junction has three or more superconducting contacts, coupling between different pairs of terminals must be taken into account and the state of the junction evolves in a phase space of higher dimensionality. Here, we study the multi-terminal inverse AC Josephson effect in a graphene sample with three superconducting terminals. We observe robust fractional Shapiro steps and correlated switching events, which can only be explained by considering the device as a completely connected Josephson network. We successfully simulate the observed behaviors using a modified two-dimensional RCSJ model. Our results suggest multi-terminal Josephson junctions are a playground to study highly-connected nonlinear networks with novel topologies.