372 research outputs found
Josephson Coupling in the Dissipative State of a Thermally Hysteretic -SQUID
Micron-sized superconducting interference devices (-SQUIDs) based on
constrictions optimized for minimizing thermal runaway are shown to exhibit
voltage oscillations with applied magnetic flux despite their hysteretic
behavior. We explain this remarkable feature by a significant supercurrent
contribution surviving deep into the resistive state, due to efficient heat
evacuation. A resistively shunted junction model, complemented by a thermal
balance determining the amplitude of the critical current, describes well all
experimental observations, including the flux modulation of the (dynamic)
retrapping current and voltage by introducing a single dimensionless parameter.
Thus hysteretic -SQUIDs can be operated in the voltage read-out mode with
a faster response. The quantitative modeling of this regime incorporating both
heating and phase dynamics paves the way for further optimization of
-SQUIDs for nano-magnetism.Comment: 10 pages, 11 figures, Revise
Proposal for detecting the shifted Cooper quartet supercurrent
The multiterminal Josephson effect aroused considerable interest recently, in
connection with theoretical and experimental evidence for correlations among
Cooper pairs, that is, the so-called Cooper quartets. It was further predicted
that the spectrum of Andreev bound states in such devices could host Weyl-point
singularities. However, the relative phase between the Cooper pair and quartet
supercurrents has not yet been addressed experimentally. Here, we propose an
experiment involving four-terminal Josephson junctions with two independent
orthogonal supercurrents, and calculate the critical current contours (CCCs)
from a multiterminal Josephson junction circuit theory. We predict a
generically -shifted contribution of both the local or nonlocal
second-order Josephson harmonics. Furthermore, we show that these lead to
marked nonconvex shapes for the CCCs in zero magnetic field, where the
dissipative state reenters into the superconducting one. Eventually, we discuss
distinctive features of the non-local Josephson processes in the CCCs. The
experimental observation of the latter could allow providing firm evidence of
the -shifted Cooper quartet current-phase relation.Comment: Third revision: manuscript in final for
Etching suspended superconducting hybrid junctions from a multilayer
A novel method to fabricate large-area superconducting hybrid tunnel
junctions with a suspended central normal metal part is presented. The samples
are fabricated by combining photo-lithography and chemical etch of a
superconductor - insulator - normal metal multilayer. The process involves few
fabrication steps, is reliable and produces extremely high-quality tunnel
junctions. Under an appropriate voltage bias, a significant electronic cooling
is demonstrated
Stochastic resonance in thermally bistable Josephson weak-links and micro-SQUIDs
Constriction-based Josephson weak-links display a thermal bi-stability
between two states exhibiting zero and finite voltages. This manifests in
experiments either as hysteresis in weak-links current voltage characteristics
or as random telegraphic signal in voltage. In the latter case, a noise-driven
amplification of a sinusoidal excitation of the device is observed, at
frequencies matching the characteristic switching frequency in telegraphic
signal, a phenomenon known as stochastic resonance. The observed behavior is
understood using a two-state model of stochastic resonance and is exploited to
illustrate an enhanced signal-to-noise-ratio in a micro-SQUID as a magnetic
field sensor.Comment: 23 pages, 7 figures, suppl. info. available on reques
Interplay of Andreev reflection and Coulomb blockade in hybrid superconducting single electron transistors
We study the interplay between Coulomb blockade and superconductivity in a
tunable superconductor-superconductor-normal metal single-electron transistor.
The device is realized by connecting the superconducting island via an oxide
barrier to the normal metal lead and with a break junction to the
superconducting lead. The latter enables Cooper pair transport and (multiple)
Andreev reflection. We show that those processes are relevant also far above
the superconducting gap and that signatures of Coulomb blockade may reoccur at
high bias while they are absent for small bias in the strong-coupling regime.
Our experimental findings agree with simulations using a master equation
approach in combination with the full counting statistics of multiple Andreev
reflection.Comment: Manuscript only, supplement available upon reques
Photon-assisted tunneling at the atomic scale: Probing resonant Andreev reflections from Yu-Shiba-Rusinov states
Tunneling across superconducting junctions proceeds by a rich variety of
processes, which transfer single electrons, Cooper pairs, or even larger
numbers of electrons by multiple Andreev reflections. Photon-assisted tunneling
combined with the venerable Tien-Gordon model has long been a powerful tool to
identify tunneling processes between superconductors. Here, we probe
superconducting tunnel junctions including an impurity-induced Yu-Shiba-Rusinov
(YSR) state by exposing a scanning tunneling microscope with a superconducting
tip to microwave radiation. We find that a simple Tien-Gordon description
describes tunneling of single electrons and Cooper pairs into the bare
substrate, but breaks down for tunneling via YSR states by resonant Andreev
reflections. We develop an improved theoretical description which is in
excellent agreement with the data. Our results establish photon-assisted
tunneling as a powerful tool to analyze tunneling processes at the atomic scale
which should be particularly informative for unconventional and topological
superconductors
Diode effect in Josephson junctions with a single magnetic atom
Current flow in electronic devices can be asymmetric with bias direction, a
phenomenon underlying the utility of diodes and known as non-reciprocal charge
transport. The promise of dissipationless electronics has recently stimulated
the quest for superconducting diodes, and non-reciprocal superconducting
devices have been realized in various non-centrosymmetric systems. Probing the
ultimate limits of miniaturization, we have created atomic-scale Pb--Pb
Josephson junctions in a scanning tunneling microscope. Pristine junctions
stabilized by a single Pb atom exhibit hysteretic behavior, confirming the high
quality of the junctions, but no asymmetry between the bias directions.
Non-reciprocal supercurrents emerge when inserting a single magnetic atom into
the junction, with the preferred direction depending on the atomic species.
Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle
currents flowing via Yu-Shiba-Rusinov (YSR) states inside the superconducting
energy gap. Our results open new avenues for creating atomic-scale Josephson
diodes and tuning their properties through single-atom manipulation
Diode effect in Josephson junctions with a single magnetic atom
Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes1 and known as non-reciprocal charge transport2. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems3,4,5,6,7,8,9,10. Here we investigate the ultimate limits of miniaturization by creating atomic-scale Pb–Pb Josephson junctions in a scanning tunnelling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behaviour, confirming the high quality of the junctions, but no asymmetry between the bias directions. Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing by means of electron–hole asymmetric Yu–Shiba–Rusinov states inside the superconducting energy gap and identify a new mechanism for diode behaviour in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation
Superconductivity in a single C60 transistor
Single molecule transistors (SMTs) are currently attracting enormous
attention as possible quantum information processing devices. An intrinsic
limitation to the prospects of these however is associated to the presence of a
small number of quantized conductance channels, each channel having a high
access resistance of at best =12.9 k. When the
contacting leads become superconducting, these correlations can extend
throughout the whole system by the proximity effect. This not only lifts the
resistive limitation of normal state contacts, but further paves a new way to
probe electron transport through a single molecule. In this work, we
demonstrate the realization of superconducting SMTs involving a single C60
fullerene molecule. The last few years have seen gate-controlled Josephson
supercurrents induced in the family of low dimensional carbon structures such
as flakes of two-dimensional graphene and portions of one-dimensional carbon
nanotubes. The present study involving a full zero-dimensionnal fullerene
completes the picture.Comment: 12 pages, 3 figure
Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS
The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured
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