81 research outputs found
Shadow epitaxy for in-situ growth of generic semiconductor/superconductor devices
Uniform, defect-free crystal interfaces and surfaces are crucial ingredients
for realizing high-performance nanoscale devices. A pertinent example is that
advances in gate-tunable and topological superconductivity using
semiconductor/superconductor electronic devices are currently built on the hard
proximity-induced superconducting gap obtained from epitaxial indium
arsenide/aluminium heterostructures. Fabrication of devices requires selective
etch processes; these exist only for InAs/Al hybrids, precluding the use of
other, potentially superior material combinations. We present a crystal growth
platform -- based on three-dimensional structuring of growth substrates --
which enables synthesis of semiconductor nanowire hybrids with in-situ
patterned superconductor shells. This platform eliminates the need for etching,
thereby enabling full freedom in choice of hybrid constituents. We realise and
characterise all the most frequently used architectures in superconducting
hybrid devices, finding increased yield and electrostatic stability compared to
etched devices, along with evidence of ballistic superconductivity. In addition
to aluminium, we present hybrid devices based on tantalum, niobium and
vanadium.
This is the submitted version of the manuscript. The accepted, peer reviewed
version is available from Advanced Materials:
http://doi.org/10.1002/adma.201908411
Previous title: Shadow lithography for in-situ growth of generic
semiconductor/superconductor device
Engineering Hybrid Epitaxial InAsSb/Al Nanowire Materials for Stronger Topological Protection
The combination of strong spin-orbit coupling, large -factors, and the
coupling to a superconductor can be used to create a topologically protected
state in a semiconductor nanowire. Here we report on growth and
characterization of hybrid epitaxial InAsSb/Al nanowires, with varying
composition and crystal structure. We find the strongest spin-orbit interaction
at intermediate compositions in zincblende InAsSb nanowires,
exceeding that of both InAs and InSb materials, confirming recent theoretical
studies \cite{winkler2016topological}. We show that the epitaxial InAsSb/Al
interfaces allows for a hard induced superconducting gap and 2 transport in
Coulomb charging experiments, similar to experiments on InAs/Al and InSb/Al
materials, and find measurements consistent with topological phase transitions
at low magnetic fields due to large effective -factors. Finally we present a
method to grow pure wurtzite InAsSb nanowires which are predicted to exhibit
even stronger spin-orbit coupling than the zincblende structure.Comment: 10 pages and 5 figure
Temperature Induced Shifts of Yu-Shiba-Rusinov Resonances in Nanowire-Based Hybrid Quantum Dots
The strong coupling of a superconductor to a spinful quantum dot results in
Yu-Shiba-Rusinov (YSR) discrete subgap excitations. In isolation and at zero
temperature, the excitations are resonances. In transport experiments,
however, they show as broad differential conductance peaks. We obtain the
lineshape of the peaks and their temperature dependence in
superconductor-quantum-dot-metal (S-QD-N) nanowire-based devices. Unexpectedly,
we find that the peaks shift in energy with temperature, with the shift
magnitude and sign depending on ground state parity and bias voltage.
Additionally, we empirically find a power-law scaling of the peak area versus
temperature. These observations are not explained by current models
Heat dissipation mechanisms in hybrid superconductor-semiconductor devices revealed by Joule spectroscopy
Understanding heating and cooling mechanisms in mesoscopic
superconductor-semiconductor hybrid devices is crucial for their application in
quantum technologies. Owing to the poor thermal conductivity of typical
devices, heating effects can drive superconducting-to-normal phase transitions
even at low applied bias, observed as sharp conductance dips through the loss
of Andreev excess currents. Tracking such dips across magnetic field, cryostat
temperature, and applied microwave power, which constitutes Joule spectroscopy,
allows to uncover the underlying cooling bottlenecks in different parts of a
device. By applying this technique, we analyze heat dissipation in devices
based on full-shell InAs-Al nanowires and reveal that superconducting islands
are strongly susceptible to heating as their cooling is limited by the rather
inefficient electron-phonon coupling, as opposed to grounded superconductors
that primarily cool by quasiparticle diffusion. Our measurements indicate that
powers as low as 50-150 pW are able to fully suprpress the superconductivity of
an island. Finally, we show that applied microwaves lead to similar heating
effects as DC signals, and explore the interplay of the microwave frequency and
the effective electron-phonon relaxation time.Comment: 9 pages, 4 figure
Utilizing a Suited Manikin Test Apparatus and Space Suit Ventilation Loop to Evaluate Carbon Dioxide Washout
NASA is pursuing technology development of an Advanced Extravehicular Mobility Unit (AEMU) which is an integrated assembly made up of primarily a pressure garment system and a portable life support subsystem (PLSS). The PLSS is further composed of an oxygen subsystem, a ventilation subsystem, and a thermal subsystem. One of the key functions of the ventilation system is to remove and control the carbon dioxide (CO2) delivered to the crewmember. Carbon dioxide washout is the mechanism by which CO2 levels are controlled within the space suit helmet to limit the concentration of CO2 inhaled by the crew member. CO2 washout performance is a critical parameter needed to ensure proper and robust designs that are insensitive to human variabilities in a space suit. A suited manikin test apparatus (SMTA) was developed to augment testing of the PLSS ventilation loop in order to provide a lower cost and more controlled alternative to human testing. The CO2 removal function is performed by the regenerative Rapid Cycle Amine (RCA) within the PLSS ventilation loop and its performance is evaluated within the integrated SMTA and Ventilation Loop test system. This paper will provide a detailed description of the schematics, test configurations, and hardware components of this integrated system. Results and analysis of testing performed with this integrated system will be presented within this paper
Asymmetric Little-Parks Oscillations in Full Shell Double Nanowires
Little-Parks oscillations of a hollow superconducting cylinder are of
interest for flux-driven topological superconductivity in single Rashba
nanowires. The oscillations are typically symmetric in the orientation of the
applied magnetic flux. Using double InAs nanowires coated by an epitaxial
superconducting Al shell which, despite the non-centro-symmetric geometry,
behaves effectively as one hollow cylinder, we demonstrate that a small
misalignment of the applied parallel field with respect to the axis of the
nanowires can produce field-asymmetric Little-Parks oscillations. These are
revealed by the simultaneous application of a magnetic field perpendicular to
the misaligned parallel field direction. The asymmetry occurs in both the
destructive regime, in which superconductivity is destroyed for half-integer
quanta of flux through the shell, and in the non-destructive regime, where
superconductivity is depressed but not fully destroyed at these flux values.Comment: 9 pages, 3 figure
Direct Activation of STING in the Tumor Microenvironment Leads to Potent and Systemic Tumor Regression and Immunity
SummarySpontaneous tumor-initiated T cell priming is dependent on IFN-β production by tumor-resident dendritic cells. On the basis of recent observations indicating that IFN-β expression was dependent upon activation of the host STING pathway, we hypothesized that direct engagement of STING through intratumoral (IT) administration of specific agonists would result in effective anti-tumor therapy. After proof-of-principle studies using the mouse STING agonist DMXAA showed a potent therapeutic effect, we generated synthetic cyclic dinucleotide (CDN) derivatives that activated all human STING alleles as well as murine STING. IT injection of STING agonists induced profound regression of established tumors in mice and generated substantial systemic immune responses capable of rejecting distant metastases and providing long-lived immunologic memory. Synthetic CDNs have high translational potential as a cancer therapeutic
Growth of InAs Wurtzite Nanocrosses from Hexagonal and Cubic Basis
Epitaxially
connected nanowires allow for the design of electron
transport experiments and applications beyond the standard two terminal
device geometries. In this Letter, we present growth methods of three
distinct types of wurtzite structured InAs nanocrosses via the vapor–liquid–solid
mechanism. Two methods use conventional wurtzite nanowire arrays as
a 6-fold hexagonal basis for growing single crystal wurtzite nanocrosses.
A third method uses the 2-fold cubic symmetry of (100) substrates
to form well-defined coherent inclusions of zinc blende in the center
of the nanocrosses. We show that all three types of nanocrosses can
be transferred undamaged to arbitrary substrates, which allows for
structural, compositional, and electrical characterization. We further
demonstrate the potential for synthesis of as-grown nanowire networks
and for using nanowires as shadow masks for in situ fabricated junctions
in radial nanowire heterostructures
Parallel InAs nanowires for Cooper pair splitters with Coulomb repulsion
Hybrid nanostructures consisting of two parallel InAs nanowires connected by an epitaxially grown superconductor (SC) shell recently became available. Due to the defect-free SC-semiconductor interface and the two quasi-one-dimensional channels being close by, these platforms can be utilized to spatially separate entangled pairs of electrons by using quantum dots (QD) in the so-called Cooper pair splitting (CPS) process. The minimized distance between the QDs overcomes the limitations of single-wire-based geometries and can boost the splitting efficiency. Here we investigate CPS in such a device where strong inter-dot Coulomb repulsion is also present and studied thoroughly. We analyze theoretically the slight reduction of the CPS efficiency imposed by the Coulomb interaction and compare it to the experiments. Despite the competition between crossed Andreev reflection (CAR) and inter-wire capacitance, a significant CPS signal is observed indicating the dominance of the superconducting coupling. Our results demonstrate that the application of parallel InAs nanowires with epitaxial SC is a promising route for the realization of parafermionic states relying on enhanced CAR between the wires
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