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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. [ABSTRACT FROM AUTHOR]

Over many years, great efforts have been made to develop new fluids for heat transfer applications. In this paper, the thermal conductivity (TC) and viscosity of SiO2–P25 TiO2 (SiO2–P25) hybrid nanofluids were investigated for different nanoparticle volume concentrations (0.5, 1.0 and 1.5 vol%) at five various temperatures (20, 30, 40, 50 and 60 °C). The mixture ratio (SiO2:P25) in all prepared hybrid nanofluids was 1:1. Besides, pure SiO2, P25 nanofluids were prepared with the same concentrations for comparison with the hybrid nanofluids. The base fluid used for the preparation of nanofluids was a mixture of deionized water and ethylene glycol at a ratio of 5:1. Before preparing the nanofluids, the nanoparticles were analyzed with energy-dispersive X-ray analysis, scanning electron microscope, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The zeta potentials of the prepared nanofluids except SiO2 nanofluids were above 30 mV. These nanofluids were visually observed for stability in many days. The TC enhancement of the hybrid nanofluid was higher than the pure nanofluid. In particular, with 1.0 vol% concentration, the maximum enhancement of SiO2, P25 and SiO2–P25 nanofluids were 7.5%, 9.9% and 10.5%, respectively. The rheology of the nanofluids was Newtonian. The viscosity increment of SiO2, P25 and hybrid nanofluids were 19%, 32% and 24% with 0.5 vol% concentration. A new correlation was developed for the TC and dynamic viscosity of SiO2–P25 hybrid nanofluid. [ABSTRACT FROM AUTHOR]

Detecting conductance quantization in graphene nanostructures turned out more challenging than expected. The observation of well-defined conductance plateaus through graphene nanoconstrictions so far has only been accessible in the highest quality suspended or h-BN encapsulated devices. However, reaching low conductance quanta in zero magnetic field, is a delicate task even with such ultra-high mobility devices. Here, we demonstrate a simple AFM-based nanopatterning technique for defining graphene constrictions with high precision (down to 10 nm width) and reduced edge-roughness (+/−1 nm). The patterning process is based on the in-plane mechanical cleavage of graphene by the AFM tip, along its high symmetry crystallographic directions. As-defined, narrow graphene constrictions with improved edge quality enable an unprecedentedly robust QPC operation, allowing the observation of conductance quantization even on standard SiO2/Si substrates, down to low conductance quanta. Conductance plateaus, were observed at n × e2/h, evenly spaced by 2 × e2/h (corresponding to n = 3, 5, 7, 9, 11) in the absence of an external magnetic field, while spaced by e2/h (n = 1, 2, 3, 4, 5, 6) in 8 T magnetic field. [ABSTRACT FROM AUTHOR]

A new electrospinning process was developed for preparing TiO2 nanofibers using a water-soluble Ti-precursor, [bis(kappa1O-hydroxo)(bis(kappa2O,O′-lactato)titanium(IV)] commonly known as titanium(IV) bis (ammonium lactato) dihydroxide (TiBALDH). The importance of the study is justified by the fact that Ti-precursors used for electrospinning, sol–gel, hydrothermal and other fiber synthesis processes are mostly non-water soluble. Accordingly, anatase TiO2 nanofibers of diameter between 20 and 140 nm were synthesized by electrospinning and annealing. Polyvinylpyrrolidone (PVP) and different concentrations of TiBALDH were dissolved in a mixture of water, ethyl alcohol and acetic acid to optimize the electrospinning conditions. The thermal decomposition and fragmentation of PVP, TiBALDH and the fibers with 50% mass fraction of TiBALDH were studied by TGA-MS measurements. The fibers were then annealed at 1 °C min−1 until 600 °C. The TiO2 fibers were characterized using SEM–EDX, FTIR and XRD [ABSTRACT FROM AUTHOR]

Recent years have brought an explosion of activities in the research of topological aspects of condensed-matter systems. Topological phases of matter are accompanied by protected surface states or exotic degenerate excitations such as Majorana modes or Haldane's localized spinons. Topologically protected degeneracies can, however, also appear in the bulk. An intriguing example is provided by Weyl semimetals, where topologically protected electronic band degeneracies and exotic surface states emerge even in the absence of interactions. Here we demonstrate experimentally and theoretically that Weyl degeneracies appear naturally in an interacting quantum dot system, for specific values of the external magnetic field. These magnetic Weyl points are robust against spin–orbit coupling unavoidably present in most quantum dot devices. Our transport experiments through an InAs double-dot device placed in magnetic field reveal the presence of a pair of Weyl points, exhibiting a robust ground-state degeneracy and a corresponding protected Kondo effect. Weyl semimetals are a class of crystalline materials whose electronic band structure exhibits topologically protected degeneracy points, known as Weyl points. Here, the authors demonstrate both theoretically and experimentally that Weyl points can also be present in the magnetic-field dependent spectrum of a double quantum dot system, enjoying a similar topological protection. [ABSTRACT FROM AUTHOR]