Andreev processes in mesoscopic multi-terminal graphene Josephson junctions

Abstract

There is growing interest in using multi-terminal Josephson junctions (MTJJs) as a platform to artificially emulate topological phases and to investigate complex superconducting mechanisms such as quartet and multiplet Cooper pairings. Current experimental signatures in MTJJs have led to conflicting interpretations of the salient features. In this work, we report a collaborative experimental and theoretical investigation of graphene-based four-terminal Josephson junctions. We observe resonant features in the differential resistance maps that resemble those ascribed to multiplet Cooper pairings. To understand these features, we model our junctions using a circuit network of coupled two-terminal resistively and capacitively shunted junctions (RCSJs). Under appropriate bias current, the model predicts that supercurrent flow between two terminals in a four-terminal geometry may be represented as a sinusoidal function of a weighted sum of the superconducting phases. We find that the resonant features generated by the RCSJ model are insensitive to the diffusive or ballistic form of the current-phase relation and junction transparency. Our study suggests that differential resistance measurements alone are insufficient to conclusively distinguish resonant Andreev reflection processes from semi-classical circuit-network effects.

Reconfigurable magnetic-field-free superconducting diode effect in multi-terminal Josephson junctions

“…Figure 1A shows an atomic force microscope (AFM) image of a representative four-terminal JJ. We characterize the junction in two asymmetric bias-current configurations (see our prior work (29) and fig.…”

Quantum interferometer for quartets in superconducting three-terminal Josephson junctions

“…Regarding experiments, an important question is about the interpretation of transport anomalies observed when a TTJ is biased at the voltages 0, V, −V [43,45,47,[53][54][55]. A conservative explanation involves the synchronization of AC Josephson currents flowing across each of the junctions polarized at V and −V , respectively [59].…”