The current-phase relation (CPR) of a Josephson junction (JJ) determines how the supercurrent evolves with the superconducting phase difference across the junction. Knowledge of the CPR is essential ...in order to understand the response of a JJ to various external parameters. Despite the rising interest in ultraclean encapsulated graphene JJs, the CPR of such junctions remains unknown. Here, we use a fully gate-tunable graphene superconducting quantum intereference device (SQUID) to determine the CPR of ballistic graphene JJs. Each of the two JJs in the SQUID is made with graphene encapsulated in hexagonal boron nitride. By independently controlling the critical current of the JJs, we can operate the SQUID either in a symmetric or asymmetric configuration. The highly asymmetric SQUID allows us to phase-bias one of the JJs and thereby directly obtain its CPR. The CPR is found to be skewed, deviating significantly from a sinusoidal form. The skewness can be tuned with the gate voltage and oscillates in antiphase with Fabry-Pérot resistance oscillations of the ballistic graphene cavity. We compare our experiments with tight-binding calculations that include realistic graphene–superconductor interfaces and find a good qualitative agreement.
This study reports on the solution combustion synthesis of two different ternary niobium oxides, namely, p-CuNb2O6 and n-ZnNb2O6. Such ternary oxides are attractive candidates in the “Holy Grail” ...search for efficient and stable semiconductors for solar energy conversion and environmental remediation. We demonstrate how this time- and energy-efficient method is capable of synthesizing high surface area and crystalline nanoparticles of the above compounds with enhanced optoelectronic properties. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV–visible and Raman spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure of these oxides was probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon to electron conversion efficiency vs wavelength). The obtained bandgap energy values (1.9 and 3.2 eV for the Cu- and Zn-containing compounds, respectively) were in reasonable agreement with those obtained via electronic structure calculations (2.07 and 3.53 eV). Finally, p-CuNb2O6 showed promising activity for the PEC reduction of CO2, while n-ZnNb2O6 was active for sulfite and water photooxidation.
When a single molecule is connected to external electrodes by linker groups, the connectivity of the linkers to the molecular core can be controlled to atomic precision by appropriate chemical ...synthesis. Recently, the connectivity dependence of the electrical conductance and Seebeck coefficient of single molecules has been investigated both theoretically and experimentally. Here, we study the connectivity dependence of the Wigner delay time of single-molecule junctions and connectivity dependence of superconducting proximity effects, which occur when the external electrodes are replaced by superconductors. Although absolute values of transport properties depend on complex and often uncontrolled details of the coupling between the molecule and electrodes, we demonstrate that ratios of transport properties can be predicted using tables of “magic numbers,” which capture the connectivity dependence of superconducting proximity effects and Wigner delay times within molecules. These numbers are calculated easily, without the need for large-scale computations. For normal–molecule–superconducting junctions, we find that the electrical conductance is proportional to the fourth power of their magic numbers, whereas for superconducting–molecule–superconducting junctions, the critical current is proportional to the square of their magic numbers. For more conventional normal–molecule–normal junctions, we demonstrate that delay time ratios can be obtained from products of magic number tables.
Theory of snake states in graphene Oroszlány, L.; Rakyta, P.; Kormányos, A. ...
Physical review. B, Condensed matter and materials physics,
02/2008, Letnik:
77, Številka:
8
Journal Article
•Chemically immobilized laccase enzyme on magnetite nanoparticles is presented.•Modified nanoparticles were entrapped in conducting polymer matrix.•Bio-electrocatalytic effect was evidenced in the ...oxygen reduction reaction.•The method may serve as a general platform for enzyme incorporation.•New avenue for conducting polymer based biocatalytic electrodes.
Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioactive component. In this study, a novel and efficient method for specific binding of laccase enzyme onto magnetite nanoparticles (NPs) is presented. The interaction between the chemically modified magnetite NPs and the enzyme was evidenced by both infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the enzyme-coated magnetite NPs were successfully incorporated into polypyrrole (PPy) matrix during galvanostatic electropolymerization. The encapsulation of laccase covered NPs was proved by EQCN, TEM, and FT-IR spectroscopy; whereas the electrochemical behaviour of the formed bionanocomposite was characterized by cyclic voltammetry. In oxygen saturated solution a cathodic charge surplus was observed, related to the electrochemical reduction of oxygen. This surplus was two times higher in the case of the laccase containing layer compared to its only magnetite containing counterpart. Kinetic aspects of the oxygen reduction reaction (ORR) on the laccase containing films were investigated by hydrodynamic voltammetry, and the four-electron route was found to be exclusive, which is promising from the fuel cell perspective. Such synergistic combination of inorganic NPs and enzymes may open new avenues in the application of these bio-nanocomposite materials.
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