We investigate the critical current, I C , of ballistic Josephson junctions made of encapsulated graphene/boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, I C is found to scale as ∝ exp(−k B T /δE). The extracted energies δE are independent of the carrier density and proportional to the level spacing of the ballistic cavity, as determined from Fabry-Perot oscillations of the junction normal resistance. As T → 0 the critical current of a long (or short) junction saturates at al level determined by the product of δE (or ∆) and the number of the junction's transversal modes.1 arXiv:1604.07320v3 [cond-mat.mes-hall] Oct 2016Encapsulated graphene/boron-nitride heterostructures emerged in the past year as a medium of choice for studying proximity-induced superconductivity in the ultra-clean limit [1][2][3][4]. These junctions support the ballistic propagation of superconducting currents across micron-scale graphene channels, and their critical current is gate-tunable across several orders of magnitude. In these devices, a rich phenomenology arises from the interplay of superconductivity with ballistic transport [1], cyclotron motion [2], and even the quantum Hall effect at high magnetic field [4]. In a superconductor -normal metal -superconductor (SNS) junction, single particles in the N region cannot enter the superconductor and therefore experience Andreev reflections at each S-N interface. This results in Andreev bound states (ABS), which are capable of 2 carrying superconducting current across the N region. In long ballistic junctions, the energy spectrum of the ABS is quantized with a level spacing of T is independent of V G . In the case of long ballistic graphene junctions, the inverse slope δE is expected to be independent of the carrier density and inversely proportional to L.In this work we study several ballistic junctions of different length and demonstrate that the temperature dependence of the critical current dramatically differs in the long and short regimes. For long junctions, we observe an exponential scaling of the current through the [5, 6,10,11]. Note that in graphene v F is a constant, and δE is expected to be independent of the carrier density or the mobility , 17-21], which could be attributed to either underdamped junction dynamics [8,20], or to the self-heating by the retrapping current [1,23]. As discussed in the supplementary material, the second scenario is more likely for most of the range studied here. Based on the measurements of the switching statistics [16,[24][25][26], in the following we will use the switching current to represent the true critical current of the junction, I C .In the hole-doped regime, the reflections of ballistic charge carriers from the n-doped contact interfaces yield the quantum ("Fabry-Perot") interference. A very similar oscillation pattern could be observed in the dependence of both the the normal conductance, G N , and the critica...

We investigate the electronic properties of ballistic planar Josephson junctions with multiple superconducting terminals. Our devices consist of monolayer graphene encapsulated in boron nitride with molybdenum-rhenium contacts. Resistance measurements yield multiple resonant features, which are attributed to supercurrent flow among adjacent and non-adjacent Josephson junctions. In particular, we find that superconducting and dissipative currents coexist within the same region of graphene. We show that the presence of dissipative currents primarily results in electron heating and estimate the associated temperature rise. We find that the electrons in encapsulated graphene are efficiently cooled through the electron-phonon coupling.

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Wood is a natural renewable material with a porous structure widely used in construction, furniture, and interior decoration, yet its intrinsic flammability poses safety risks. Therefore, environmentally friendly flame retardants have received increasing attention. In this study, a water-soluble flame retardant, consisting of bio-resourced phytic acid (PA), hydrolyzed collagen (HC), and glycerol (GL), was used to improve the flame retardancy of wood (“PHG/wood”) through full cell vacuum-pressure impregnation. Morphology and Fourier transform infrared analysis results show that the flame retardant impregnated the wood and adhered evenly to the wood vessels. A PA/HC/GL ratio of 3:1:1 (concentration of the flame retardant solution = 30%) maximized the limiting oxygen index (LOI, 41%) and weight gain (51.32%) for PHG-C30/wood. The flame retardant formed an expansive layer after heating, and the treated wood showed an improved combustion safety performance such that the fire performance index and residue of PHG-C30/wood were 75 and 126.8% higher compared with that of untreated wood, respectively. The peak and total heat release were also significantly reduced by 54.7 and 47.7%, respectively. The PHG/wood exhibited good carbon-forming performance and a high degree of graphitization after combustion. The dense carbon layer provides condensed phase protective action, and non-combustible volatile gases, such as H2O, CO2, and NH3, are released simultaneously to dilute the fuel load in the gas phase. Thus, PHG is shown to be an effective flame retardant for wood.

Summary: Star‐like hydroxypropyl lignin (HL) was compounded into soy protein isolated (SPI) to develop a potential biodegradable plastic with better mechanical performance than pure sheet‐SPI. The structure and properties of the composite materials were characterized by WAXD, DSC, SEM, TEM and tensile tests. The addition of just 2 wt.‐% HL resulted in tensile strength (σb) of 16.8 MPa, 2.3 times that of pure sheet‐SPI, with no accompanying decrease in elongation at break as a result of strong interaction and with good miscibility among components. As the HL content increased, the HL molecules could self‐aggregate as oblate supramolecular domains, while the stronger interactions between HL and glycerol resulted in the detaching of glycerol from the SPI matrix. It can be concluded that the insertion of HL as single molecules into the SPI matrix would provide materials with optimum mechanical properties. Compared with other lignin/SPI composites, the stretching chains on HL play a key role in the improvement of mechanical properties because of a stronger adhesion of HL onto the SPI matrix as well as the interpenetration of SPI into supramolecular HL domains.Schematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate.imageSchematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate.