Gate-tunable junctions are key elements in quantum devices based on hybrid semiconductor–superconductor materials. They serve multiple purposes ranging from tunnel spectroscopy probes to voltage-controlled qubit operations in gatemon and topological qubits. Common to all is that junction transparency plays a critical role. In this study, we grow single-crystalline InAs, InSb, and InAs1–x Sb x semiconductor nanowires with epitaxial Al, Sn, and Pb superconductors and in situ shadowed junctions in a single-step molecular beam epitaxy process. We investigate correlations between fabrication parameters, junction morphologies, and electronic transport properties of the junctions and show that the examined in situ shadowed junctions are of significantly higher quality than the etched junctions. By varying the edge sharpness of the shadow junctions, we show that the sharpest edges yield the highest junction transparency for all three examined semiconductors. Further, critical supercurrent measurements reveal an extraordinarily high I C R N, close to the KO-2 limit. This study demonstrates a promising engineering path toward reliable gate-tunable superconducting qubits.

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Polyvinyl-pyrrolidone (PVP) loaded with different fractions of dispersed nanographene platelets (NGP) were studied by Broadband Dielectric Spectroscopy in the frequency range from 1 mHz to 1 MHz. Complex permittivity and dynamic ac conductivity as a function of frequency, temperature and composition were explored. The concentration-dependent insulator-to-conductor transition was traced through dependence of the dc conductivity and the onset of the dispersive ac ac conductivity. The temperature evolution of the dielectric spectra, below and above the fractional threshold exhibits different dynamics and signs the critical percolation threshold. Percolation is dictated by quantum penetration of the effective potential barrier set by the polymer matrix operating in parallel with conduction along physical contact of NGP, in accordance with predictions for systems consisting of a semi-conducting matrix and dispersed conducting inclusions.* Corresponding author; e-mail address: antpapa@phys.uoa.gr 2 Functional polymers with dispersed nano-structures exhibit properties of significant technological importance, broad applicability and low production cost. Polyvinyl-pyrrolidone (PVP) is a polymer wide known for its pharmaceutical applications. It can be used as binder, coating and disintegrate for tablets stabilizer [1]. PVP is easily dissolved in water; both PVP and water are non-toxic, environmentally friendly and bio-compatible materials. Graphene is an excellent conductor of electricity and can be dispersed into water. Nano-graphene platelets combine the advantageous properties of graphene and the low production cost (e.g., in relation with single layered graphene). Thus, controlling the PVP/NGP composition, one can tune the properties of the composite, respectively, and achieve the desired optimum properties respectively. In this way, novel ambitious devices can be innovated. For example, water solutions PVP/ NGP composite can be used as bio-compatible link between electrodes and skin or tissues. As a result, various coated functional polymers with graphene [2, 3] have been prepared in order to analyse the mechanisms of charge transfer [4], to find the critical nanoparticle concentration to achieve percolation of electric charge carriers along the volume of the composite [5,6,7] and generally to inspect the electrical properties for those various matrices.Lastly, PVA (polyvinyl-alcohol) is a relevant material with polyvinyl-pyrrolidone that has been studied significantly [8]. In such studies, the dc conductivity vs composition is examined to find the percolation threshold. Standard percolation theories [9] assume that the host matrix is a perfect insulator, which is an abrupt assumption in many real systems. Recent progresses on percolation phenomena in systems with matrixes that can be penetrated by electron quantum mechanical tunneling [10] describe better PVP/NGP composites.Aqueous polymer solutions were formed by dissolving PVP K30 (ASG SCIENTIFICCAS 9003-39-8) in de-ionized doubly distilled water and aque...

Hybrid semiconductor−superconductor nanowires constitute a pervasive platform for studying gate-tunable superconductivity and the emergence of topological behavior. Their low dimensionality and crystal structure flexibility facilitate unique heterostructure growth and efficient material optimization, crucial prerequisites for accurately constructing complex multicomponent quantum materials. Here, we present an extensive study of Sn growth on InSb, InAsSb, and InAs nanowires and demonstrate how the crystal structure of the nanowires drives the formation of either semimetallic α-Sn or superconducting β-Sn. For InAs nanowires, we observe phasepure superconducting β-Sn shells. However, for InSb and InAsSb nanowires, an initial epitaxial α-Sn phase evolves into a polycrystalline shell of coexisting α and β phases, where the β/ α volume ratio increases with Sn shell thickness. Whether these nanowires exhibit superconductivity or not critically relies on the β-Sn content. Therefore, this work provides key insights into Sn phases on a variety of semiconductors with consequences for the yield of superconducting hybrids suitable for generating topological systems.