Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to ...superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale.
Sensitive microwave detectors are essential in radioastronomy
, dark-matter axion searches
and superconducting quantum information science
. The conventional strategy to obtain higher-sensitivity ...bolometry is the nanofabrication of ever smaller devices to augment the thermal response
. However, it is difficult to obtain efficient photon coupling and to maintain the material properties in a device with a large surface-to-volume ratio owing to surface contamination. Here we present an ultimately thin bolometric sensor based on monolayer graphene. To utilize the minute electronic specific heat and thermal conductivity of graphene, we develop a superconductor-graphene-superconductor Josephson junction
bolometer embedded in a microwave resonator with a resonance frequency of 7.9 gigahertz and over 99 per cent coupling efficiency. The dependence of the Josephson switching current on the operating temperature, charge density, input power and frequency shows a noise-equivalent power of 7 × 10
watts per square-root hertz, which corresponds to an energy resolution of a single 32-gigahertz photon
, reaching the fundamental limit imposed by intrinsic thermal fluctuations at 0.19 kelvin. Our results establish that two-dimensional materials could enable the development of bolometers with the highest sensitivity allowed by the laws of thermodynamics.
The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the ...quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states.
This research applies acoustic topology optimization (ATO) for noise barrier design with rigid and porous materials. Many researchers have investigated the pressure attenuation phenomena of noise ...barriers under various geometric, material, and boundary conditions. To improve the pressure attenuation performance of noise barriers, size and shape optimization have been applied, and ATO methods have been proposed that allow concurrent size, shape, and topological changes of rigid walls and cavities. Nevertheless, it is unusual to optimize the topologies of noise barriers by considering the pressure attenuation effect of a porous material. The present research develops a new ATO considering both porous and rigid materials and applies it to the discovery of optimal topologies of noise barriers composed of both materials. In the present approach, the noise absorption characteristics of porous materials are numerically modeled using the Delany–Bazley empirical material model, and we also investigate the effects of some interpolation functions on optimal material distributions. Applying the present ATO approach, we found some novel noise barriers optimized for various geometric and environmental conditions.
The present work aims to study the removal of color and COD from livestock wastewater by electrocoagulation (EC) process using Al electrodes. The Box–Behnken design and response surface methodology ...were used to investigate the effects of major operating variables and optimization conditions. The predicted values of responses obtained using the response function agree well with the experimental data. Economical operating conditions and removal efficiencies were found to be pH of 8, current density of 30mA/cm2, electrolysis time of 30min and NaCl concentration of 1g/L, and 95.2% (Y1) and 93% (Y2), respectively.
Carbon nanotubes (CNTs), either single wall carbon nanotubes (SWNTs) or multiwall carbon nanotubes (MWNTs), can improve the thermoelectric properties of poly(3,4-ethylenedioxythiophene) ...poly(styrenesulfonate) (PEDOT : PSS), but it requires addition of 30-40 wt% CNTs. We report that the figure of merit (ZT) value of PEDOT : PSS thin film for thermoelectric property is increased about 10 times by incorporating 2 wt% of graphene. PEDOT : PSS thin films containing 1, 2, 3 wt% graphene are prepared by solution spin coating method. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses identified the strong π-π interactions which facilitated the dispersion between graphene and PEDOT : PSS. The uniformly distributed graphene increased the interfacial area by 2-10 times as compared with CNT based on the same weight. The power factor and ZT value of PEDOT : PSS thin film containing 2 wt% graphene was 11.09 μW mK(-2) and 2.1 × 10(-2), respectively. This enhancement arises from the facilitated carrier transfer between PEDOT : PSS and graphene as well as the high electron mobility of graphene (200,000 cm(2) V(-1) s(-1)). Furthermore the porous structure of the thin film decreases the thermal conductivity resulting in a high ZT value, which is higher by 20% than that for a PEDOT : PSS thin film containing 35 wt% SWNTs.
In this study, we developed an acoustic topology optimization using moving morphable components (MMCs) for the design of two-dimensional sound reduction structures. MMC-based topology optimization ...has been developed for structural topology optimization; however, no extant study on the design of sound reduction structures has utilized MMC-based topology optimization. Instead of directly changing the distribution of pixel-wise materials to form the shape of a structure, MMC-based topology optimization changes the geometric and positional parameters of MMCs and forms the shape of a structure through the overlapping of MMCs. In this study, finite element analysis based on the Helmholtz equation was performed to calculate the acoustic performance of sound reduction structures. To complement the unsatisfactory performance of designs by local optimal points, we evaluated many designs optimized under different design conditions and optimization settings with respect to the original design condition. We also devised additional design procedures to improve the acoustic performance of sound reduction structures by exploring a lot of design samples modified from the designs based on MMC-based topology optimization. Owing to the rather long time required for repeated performance calculations, the performance was estimated by using a multilayer perceptron to roughly select the design samples that need to be evaluated by finite element analysis. Design examples for barrier structures and duct internal structures were considered to demonstrate the validity of the proposed approach.
The fractions of various functional groups in graphene oxide (GO) are directly related to its electrical and chemical properties and can be controlled by various reduction methods like thermal, ...chemical and optical. However, a method with sufficient controllability to regulate the reduction process has been missing. In this work, a hybrid method of thermal and joule heating processes is demonstrated where a progressive control of the ratio of various functional groups can be achieved in a localized area. With this precise control of carbon-oxygen ratio, negative differential resistance (NDR) is observed in the current-voltage characteristics of a two-terminal device in the ambient environment due to charge-activated electrochemical reactions at the GO surface. This experimental observation correlates with the optical and chemical characterizations. This NDR behavior offers new opportunities for the fabrication and application of such novel electronic devices in a wide range of devices applications including switches and oscillators.
Manipulation of Ohmic contacts in 2D transition metal dichalcogenides for enhancing the transport properties and enabling its application as a practical device has been a long‐sought goal. In this ...study, n‐type tungsten disulfide (WS2) single atomic layer to improve the Ohmic contacts of the p‐type molybdenum ditelluride (MoTe2) material is covered. The Ohmic properties, based on the lowering of Schottky barrier height (SBH) owing to the tunneling barrier effect of the WS2 monolayer, are found to be unexpectedly excellent at room temperature and even at 100 K. The improved SBH and contact resistances are 3 meV and 1 MΩ µm, respectively. The reduction in SBH and contact resistance is confirmed with temperature‐dependent transport measurements. This study further demonstrates the selective carrier transport across the MoTe2 and WS2 layers by modulating the applied gate voltage. This WS2/MoTe2 heterostructure exhibits excellent gate control over the currents of both channels (n‐type and p‐type). The on/off ratios for both the electron and hole channels are calculated as 107 and 106, respectively, indicating good carrier type modulation by the electric field of the gate electrode. The Ohmic contact resistance using the tunneling of the atomic layer can be applied to heterojunction combinations of various materials.
Innovative heterostructure consisting of a semiconducting monolayer WS2 tunneling layer and a few‐layer bottom MoTe2 is reported. By applying an appropriate gate voltage, n‐channel in WS2 monolayer and p‐channel in MoTe2 are accessed separately. Owing to single atomic thickness of WS2, the Schottky barrier and contact resistance on few‐layer MoTe2 are greatly reduced resulting in good Ohmic contact.
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