6 research outputs found
Quantum Phase Transition in a Resonant Level Coupled to Interacting Leads
An interacting one-dimensional electron system, the Luttinger liquid, is
distinct from the "conventional" Fermi liquids formed by interacting electrons
in two and three dimensions. Some of its most spectacular properties are
revealed in the process of electron tunneling: as a function of the applied
bias or temperature the tunneling current demonstrates a non-trivial power-law
suppression. Here, we create a system which emulates tunneling in a Luttinger
liquid, by controlling the interaction of the tunneling electron with its
environment. We further replace a single tunneling barrier with a
double-barrier resonant level structure and investigate resonant tunneling
between Luttinger liquids. For the first time, we observe perfect transparency
of the resonant level embedded in the interacting environment, while the width
of the resonance tends to zero. We argue that this unique behavior results from
many-body physics of interacting electrons and signals the presence of a
quantum phase transition (QPT). In our samples many parameters, including the
interaction strength, can be precisely controlled; thus, we have created an
attractive model system for studying quantum critical phenomena in general. Our
work therefore has broadly reaching implications for understanding QPTs in more
complex systems, such as cold atoms and strongly correlated bulk materials.Comment: 11 pages total (main text + supplementary
Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions
We present transport measurements
on long, diffusive, graphene-based Josephson junctions. Several junctions
are made on a single-domain crystal of CVD graphene and feature the
same contact width of ∼9 μm but vary in length from 400
to 1000 nm. As the carrier density is tuned with the gate voltage,
the critical current in these junctions ranges from a few nanoamperes
up to more than 5 μA, while the Thouless energy, <i>E</i><sub>Th</sub>, covers almost 2 orders of magnitude. Over much of
this range, the product of the critical current and the normal resistance <i>I</i><sub>C</sub><i>R</i><sub>N</sub> is found to
scale linearly with <i>E</i><sub>Th</sub>, as expected from
theory. However, the value of the ratio <i>I</i><sub>C</sub><i>R</i><sub>N</sub>/<i>E</i><sub>Th</sub> is
found to be 0.1–0.2, which much smaller than the predicted
∼10 for long diffusive SNS junctions