Evidence for π-shifted Cooper quartets and few-mode transport in PbTe nanowire three-terminal Josephson junctions
arxiv(2023)
摘要
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. This approach offers
unique possibilities that are complementary to phenomena attainable in bulk
crystals, including topological states in more than three dimensions and
real-time gate-tunability of the Hamiltonians. However, these prospects rely on
the ability to create MTJJs with non-classical multi-terminal couplings in
which only a handful of quantum modes are populated. Here, we demonstrate these
requirements by using a three-terminal Josephson junction fabricated on
selective-area-grown (SAG) PbTe nanowires. We observe signatures of a
π-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. These results establish a
platform for investigations of topological Hamiltonians based on Andreev bound
states.
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