42 research outputs found
Zero-bias conductance in carbon nanotube quantum dots
We present numerical renormalization group calculations for the zero-bias
conductance of quantum dots made from semiconducting carbon nanotubes. These
explain and reproduce the thermal evolution of the conductance for different
groups of orbitals, as the dot-lead tunnel coupling is varied and the system
evolves from correlated Kondo behavior to more weakly correlated regimes. For
integer fillings of an SU(4) model, we find universal scaling
behavior of the conductance that is distinct from the standard SU(2) universal
conductance, and concurs quantitatively with experiment. Our results also agree
qualitatively with experimental differential conductance maps.Comment: 4 pages, 5 figure
Stepwise Self-Assembly of DNA Tile Lattices Using dsDNA Bridges
The simple helical motif of double-strand DNA (dsDNA) has typically been judged to be uninteresting for assembly in DNA-based nanotechnology applications. In this letter, we demonstrate construction of superstructures consisting of heterogeneous DNA motifs using dsDNA in conjunction with more complex, cross-tile building blocks. Incorporation of dsDNA bridges in stepwise assembly processes can be used for controlling length and directionality of superstructures and is analogous to the “reprogramming” of sticky-ends displayed on the DNA tiles. Two distinct self-assembled DNA lattices, fixed-size nanoarrays, and extended 2D crystals of nanotracks with nanobridges, are constructed and visualized by high-resolution, liquid-phase atomic force microscopy
Loss and decoherence at the quantum Hall - superconductor interface
High quality type-II superconducting contacts have recently been developed to
a variety of 2D systems, allowing one to explore the superconducting proximity
in the quantum Hall (QH) regime. Inducing superconducting correlations into a
chiral system has long been viewed as a route for creating exotic topological
states and excitations. However, it appears that before these exciting
predictions could be realized, one should develop a better understanding of the
limitations imposed by the physics of real materials. Here, we perform a
systematic study of Andreev conversion at the interface between a
superconductor and graphene in the QH regime. We find that the probability of
Andreev conversion of electrons to holes follows an unexpected but clear trend:
the dependencies on temperature and magnetic field are nearly decoupled. We
discuss these trends and the role of the superconducting vortices, whose normal
cores could both absorb and dephase the individual electrons in a QH edge. Our
study may pave the road to engineering future generation of hybrid devices for
exploiting superconductivity proximity in chiral channels
Dynamical Stabilization of Multiplet Supercurrents in Multi-terminal Josephson Junctions
The dynamical properties of multi-terminal Josephson junctions have recently
attracted interest, driven by the promise of new insights into synthetic
topological phases of matter and Floquet states. This effort has culminated in
the discovery of Cooper multiplets, in which the splitting of a Cooper pair is
enabled via a series of Andreev reflections that entangle four (or more)
electrons. In this text, we show conclusively that multiplet resonances can
also emerge as a consequence of the three terminal circuit model. The
supercurrent appears due to the correlated phase dynamics at values that
correspond to the multiplet condition of applied bias. The
emergence of multiplet resonances is seen in i) a nanofabricated three-terminal
graphene Josephson junction, ii) an analog three terminal Josephson junction
circuit, and iii) a circuit simulation. The mechanism which stabilizes the
state of the system under those conditions is purely dynamical, and a close
analog to Kapitza's inverted pendulum problem. We describe parameter
considerations that best optimize the detection of the multiplet lines both for
design of future devices. Further, these supercurrents have a classically
robust energy contribution, which can be used to engineer qubits
based on higher harmonics
Graphene-based quantum Hall interferometer with self-aligned side gates
The vanishing band gap of graphene has long presented challenges for
fabricating high-quality quantum point contacts (QPCs) -- the partially
transparent p-n interfaces introduced by conventional split-gates tend to short
the QPC. This complication has hindered the fabrication of graphene quantum
Hall Fabry-P\'erot interferometers, until recent advances have allowed
split-gate QPCs to operate utilizing the highly resistive state. Here,
we present a simple recipe to fabricate QPCs by etching a narrow trench in the
graphene sheet to separate the conducting channel from self-aligned graphene
side gates. We demonstrate operation of the individual QPCs in the quantum Hall
regime, and further utilize these QPCs to create and study a quantum Hall
interferometer