255 research outputs found
Out-of-equilibrium phonons in gated superconducting switches
Recent experiments have suggested that superconductivity in metallic nanowires can be suppressed by the application of modest gate voltages. The source of this gate action has been debated and either attributed to an electric-field effect or to small leakage currents. Here we show that the suppression of superconductivity in titanium nitride nanowires on silicon substrates does not depend on the presence or absence of an electric field at the nanowire, but requires a current of high-energy electrons. The suppression is most efficient when electrons are injected into the nanowire, but similar results are obtained when electrons are passed between two remote electrodes. This is explained by the decay of high-energy electrons into phonons, which propagate through the substrate and affect superconductivity in the nanowire by generating quasiparticles. By studying the switching probability distribution of the nanowire, we also show that high-energy electron emission leads to a much broader phonon energy distribution compared with the case where superconductivity is suppressed by Joule heating near the nanowire
The systematic tunability of nanoparticle dimensions through the controlled loading of surface-deposited diblock copolymer micelles
The continuous tunability of iron oxide nanoparticle dimensions is demonstrated using the pH controlled loading of ferric nitrate from aqueous solution into polystyreneâblockâpolyacrylic acid reverse micelles deposited on a silicon substrate. Quasi-hexagonally ordered two-dimensional arrays of iron oxide nanoparticles with a systematic tunability of particle heights in the sub-10 nm regime and a constant periodicity are obtained and characterized with atomic force microscopy and x-ray photoelectron spectroscopy
Block copolymer micelles as switchable templates for nanofabrication
Block copolymer inverse micelles from polystyrene-block-poly-2-vinylpyridine (PS-b-P2VP) deposited as monolayer films onto surfaces show responsive behavior and are reversibly switchable between two states of different topography and surface chemistry. The as-coated films are in the form of arrays of nanoscale bumps, which can be transformed into arrays of nanoscale holes by switching through exposure to methanol. The use of these micellar films to act as switchable etch masks for the structuring of the underlying material to form either pillars or holes depending on the switching state is demonstrated
Spin-degeneracy breaking and parity transitions in three-terminal Josephson junctions
Harnessing spin and parity degrees of freedom is of fundamental importance
for the realization of emergent quantum devices. Nanostructures embedded in
superconductor--semiconductor hybrid materials offer novel and yet unexplored
routes for addressing and manipulating fermionic modes. Here we
spectroscopically probe the two-dimensional band structure of Andreev bound
states in a phase-controlled hybrid three-terminal Josephson junction. Andreev
bands reveal spin-degeneracy breaking, with level splitting in excess of 9 GHz,
and zero-energy crossings associated to ground state fermion parity
transitions, in agreement with theoretical predictions. Both effects occur
without the need of external magnetic fields or sizable charging energies and
are tuned locally by controlling superconducting phase differences. Our results
highlight the potential of multiterminal hybrid devices for engineering quantum
states
Zeeman and Orbital Driven Phase Transitions in Planar Josephson Junctions
We perform supercurrent and tunneling spectroscopy measurements on
gate-tunable InAs/Al Josephson junctions (JJs) in an in-plane magnetic field,
and report on phase shifts in the current-phase relation measured with respect
to an absolute phase reference. The impact of orbital effects is investigated
by studying multiple devices with different superconducting lead sizes. At low
fields, we observe gate-dependent phase shifts of up to
which are consistent with a Zeeman field coupling to highly-transmissive
Andreev bound states via Rashba spin-orbit interaction. A distinct phase shift
emerges at larger fields, concomitant with a switching current minimum and the
closing and reopening of the superconducting gap. These signatures of an
induced phase transition, which might resemble a topological transition, scale
with the superconducting lead size, demonstrating the crucial role of orbital
effects. Our results elucidate the interplay of Zeeman, spin-orbit and orbital
effects in InAs/Al JJs, giving new understanding to phase transitions in hybrid
JJs and their applications in quantum computing and superconducting
electronics
Microwave-induced conductance replicas in hybrid Josephson junctions without Floquet-Andreev states
Light-matter interaction enables engineering of non-equilibrium quantum
systems. In condensed matter, spatially and temporally cyclic Hamiltonians are
expected to generate energy-periodic Floquet states, with properties
inaccessible at thermal equilibrium. A recent work explored the tunnelling
conductance of a planar Josephson junction under microwave irradiation, and
interpreted replicas of conductance features as evidence of steady
Floquet-Andreev states. Here we realise a similar device in a hybrid
superconducting-semiconducting heterostructure, which utilises a tunnelling
probe with gate-tunable transparency and allows simultaneous measurements of
Andreev spectrum and current-phase relation of the planar Josephson junction.
We show that, in our devices, spectral replicas in sub-gap conductance emerging
under microwave irradiation are caused by photon assisted tunnelling of
electrons into Andreev states. The current-phase relation under microwave
irradiation is also explained by the interaction of Andreev states with
microwave photons, without the need to invoke Floquet states. The techniques
outlined in this study establish a baseline to distinguish photon assisted
tunnelling from Floquet-Andreev states in mesoscopic devices, a crucial
development towards understanding light-matter coupling in hybrid
nanostructures
Exercise-induced modulation of cardiac lipid content in healthy lean young men
Cardiac lipid accumulation is associated with decreased cardiac function and energy status (PCr/ATP). It has been suggested that elevated plasma fatty acid (FA) concentrations are responsible for the cardiac lipid accumulation. Therefore, the aim of the present study was to investigate if elevating plasma FA concentrations by exercise results in an increased cardiac lipid content, and if this influences cardiac function and energy status. Eleven male subjects (age 25.4 ± 1.1 years, BMI 23.6 ± 0.8 kg/m2) performed a 2-h cycling protocol, once while staying fasted and once while ingesting glucose, to create a state of high versus low plasma FA concentrations, respectively. Cardiac lipid content was measured by proton magnetic resonance spectroscopy (1H-MRS) at baseline, directly after exercise and again 4 h post-exercise, together with systolic function (by multi-slice cine-MRI) and cardiac energy status (by 31P-MRS). Plasma FA concentrations were increased threefold during exercise and ninefold during recovery in the fasted state compared with the glucose-fed state (p < 0.01). Cardiac lipid content was elevated at the end of the fasted test day (from 0.26 ± 0.04 to 0.44 ± 0.04%, p = 0.003), while it did not change with glucose supplementation (from 0.32 ± 0.03 to 0.26 ± 0.05%, p = 0.272). Furthermore, PCr/ATP was decreased by 32% in the high plasma FA state compared with the low FA state (n = 6, p = 0.014). However, in the high FA state, the ejection fraction 4 h post-exercise was higher compared with the low FA state (63 ± 2 vs. 59 ± 2%, p = 0.018). Elevated plasma FA concentrations, induced by exercise in the fasted state, lead to increased cardiac lipid content, but do not acutely hamper systolic function. Although the lower cardiac energy status is in line with a lipotoxic action of cardiac lipid content, a causal relationship cannot be proven
Flip-chip-based fast inductive parity readout of a planar superconducting island
Properties of superconducting devices depend sensitively on the parity (even
or odd) of the quasiparticles they contain. Encoding quantum information in the
parity degree of freedom is central in several emerging solid-state qubit
architectures. Yet, accurate, non-destructive, and time-resolved parity
measurement is a challenging and long-standing issue. Here we report on control
and real-time parity measurement in a superconducting island embedded in a
superconducting loop and realized in a hybrid two-dimensional heterostructure
using a microwave resonator. Device and readout resonator are located on
separate chips, connected via flip-chip bonding, and couple inductively through
vacuum. The superconducting resonator detects the parity-dependent circuit
inductance, allowing for fast and non-destructive parity readout. We resolved
even and odd parity states with signal-to-noise ratio SNR with an
integration time of s and detection fidelity exceeding 98%. Real-time
parity measurement showed state lifetime extending into millisecond range. Our
approach will lead to better understanding of coherence-limiting mechanisms in
superconducting quantum hardware and provide novel readout schemes for hybrid
qubits
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