Evidence for $\pi$-shifted Cooper quartets and few-mode transport in PbTe nanowire three-terminal Josephson junctions

TL;DR

This paper demonstrates multi-terminal Josephson junctions in PbTe nanowires showing evidence of $$-shifted Cooper quartets and few-mode transport, opening pathways for topological quantum states engineering.

Contribution

It provides experimental evidence of $$-shifted Cooper quartets and few-mode transport in three-terminal PbTe nanowire Josephson junctions, advancing multi-terminal quantum device research.

Findings

Observation of $$-shifted Josephson effect

Detection of supercurrent with non-monotonic conductance

Transport mediated by few quantum modes

Abstract

Josephson junctions are typically characterized by a single phase difference across two superconductors. This conventional two-terminal Josephson junction can be generalized to a multi-terminal device where the Josephson energy contains terms with contributions from multiple independent phase variables. Such multi-terminal Josephson junctions (MTJJs) are being considered as platforms for engineering effective Hamiltonians with non-trivial topologies, such as Weyl crossings and higher-order Chern numbers. These prospects rely on the ability to create MTJJs with non-classical multi-terminal couplings in which only a few quantum modes are populated. Here, we demonstrate these requirements in a three-terminal Josephson junction fabricated on selective-area-grown (SAG) PbTe nanowires. We observe signatures of a $\pi$-shifted Josephson effect, consistent with inter-terminal couplings mediated by four-particle quantum states called Cooper quartets. We further observe supercurrent co-existent with a non-monotonic evolution of the conductance with gate voltage, indicating transport mediated by a few quantum modes in both two- and three-terminal devices.