Explore the vast range of titles available.

To study non-magnetic and magnetic impurity effects at the superconductor-normal metal interfaces, we have measured the differential conductance dI/dV for Josephson contacts made by vanadium (V) nanoconstrictions with a different amount of hydrogen (H) and deuterium (D) impurities, which are prepared by a mechanically controllable break junction (MCBJ) technique at low temperature. Below the superconducting transition temperature TC, we have found distinct peaks within and outside the gap, known as the sub-gap structure and an over-the-gap structure respectively, due to 5% concentration of atomic H and D on V nanocontact. Moreover, the temperature dependence of dI/dV spectra represents that both structures are survived until the critical temperature TC, which is consistent with the prediction of BCS energy gap. On the other hand, a very high concentrating phase (30atom%) behaves as a normal metal.

The emergence of the nematic electronic state that breaks rotational symmetry is one of the most fascinating properties of the iron-based superconductors, and has relevance to cuprates as well. FeSe has a unique ground state in which superconductivity coexists with a nematic order without long-range magnetic ordering, providing a significant opportunity to investigate the role of nematicity in the superconducting pairing interaction. Here, to reveal how the superconducting gap evolves with nematicity, we measure the thermal conductivity and specific heat of FeSe1—xSₓ, in which the nematicity is suppressed by isoelectronic sulfur substitution and a nematic critical point (NCP) appears at xc ≈ 0.17. We find that, in the whole nematic regime (0 < x <0.17), the field dependence of two quantities consistently shows two-gap behavior; one gap is small but highly anisotropic with deep minima or line nodes, and the other is larger and more isotropic. In stark contrast, in the tetragonal regime (x = 0.20), the larger gap becomes strongly anisotropic, demonstrating an abrupt change in the superconducting gap structure at the NCP. Near the NCP, charge fluctuations of dxz and dyz orbitals are enhanced equally in the tetragonal side, whereas they develop differently in the orthorhombic side. Our observation therefore directly implies that the orbital-dependent nature of the nematic fluctuations has a strong impact on the superconducting gap structure and hence on the pairing interaction.

The structural complexity, especially canopy and gap structure, of old‐growth forests affects the spatial variation of soil respiration (Rs). Without considering this variation, the upscaling of Rs from field measurements to the forest site will be biased. The present study examined responses of Rs to soil temperature (Ts) and water content (W) in canopy and gap areas, developed the best fit modelof Rs and used the unique spatial patterns of Rs and crown closure to upscale chamber measurements to the site scale in an old‐growth beech‐oak forest. Rs increased with an increase in Ts in both gap and canopy areas, but the effect of W on Rs was different between the two areas. The generalized linear model (GLM) analysis identified that an empirical model of Rs with thecoupling of Ts and W was better than an exponential model of Rs with only Ts. Moreover, because of different responses of Rs to W between canopy and gap areas, it was necessary to estimate Rs in these areas separately. Consequently, combining the spatial patterns of Rs and the crown closure could allow upscaling of Rs from chamber‐based measurements to the whole site in the present study.

Low-temperature specific heat (SH) is measured for the 12442-type KCa 2 Fe 4 As 4 F 2 single crystal under different magnetic fields. A clear SH jump with the height of Δ C / T | T c = 130 mJ moL −1 K −2 is observed at the superconducting transition temperature T c . It is found that the electronic SH coefficient ∆ γ ( H ) quickly increases when the field is in the low-field region below 3 T and then considerably slows down the increase with a further increase in the field, which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s). The temperature-dependent SH data indicate the presence of the T 2 term, which supplies further information and supports the picture with a line-nodal gap structure. Moreover, the onset point of the SH transition remains almost unchanged under the field as high as 9 T, which is similar to that observed in cuprates, and places this system in the middle between the BCS limit and the Bose-Einstein condensation.

In this article, we report on video-rate identification of very low-cost tags in the terahertz (THz) domain. Contrary to barcodes, Radio Frequency Identification (RFID) tags, or even chipless RFID tags, operate in the Ultra-Wide Band (UWB). These THz labels are not based on a planar surface pattern but are instead embedded, thus hidden, in the volume of the product to identify. The tag is entirely made of dielectric materials and is based on a 1D photonic bandgap structure, made of a quasi-periodic stack of two different polyethylene-based materials presenting different refractive indices. The thickness of each layer is of the order of the THz wavelength, leading to an overall tag thickness in the millimetre range. More particularly, we show in this article that the binary information coded within these tags can be rapidly and reliably identified using a commercial terahertz Time Domain Spectroscopy (THz-TDS) system as a reader. More precisely, a bit error rate smaller than 1% is experimentally reached for a reading duration as short as a few tens of milliseconds on an 8 bits (~40 bits/cm2) THID tag. The performance limits of such a tag structure are explored in terms of both dielectric material properties (losses) and angular acceptance. Finally, realistic coding capacities of about 60 bits (~300 bits/cm2) can be envisaged with such tags.

In this paper, we consider quantum graphs corresponding to zigzag carbon nanotubes with finite number of impurities. Recall that the quantum graph for a zigzag carbon nanotube without impurities is the triplet of the metric graph for the zigzag carbon nanotube Γ N with N -zigzags, the Schrödinger operator on Γ N and the Kirchhoff–Neumann vertex condition. To express impurities, we utilize the δ -type vertex condition. In this paper, we study the case where the impurities are located symmetrically with respect to the rotation as a finite number of impurity rings. After we construct a general spectral theory for the setting, we give an exact formulae for the number of negative eigenvalues in the case of a single ring in terms of the strength β of impurities. Throughout this paper, we shall find an interesting difference between zigzag carbon nanotubes and the one-dimensional Schrödinger operator with the δ point interactions.

In this study, the porous ultrathin graphitic carbon nitride (CN) nanosheets with rich C and nitrogen defects were prepared by one-step calcining the mixture of melamine and glucose (Glu) in air atmosphere (Glu-CN). Introducing simultaneously rich C atoms and nitrogen defects into CN structures continuously modulates the bandgaps from 2.67 to 1.81 eV of CN photocatalysts. Due to large surface area, more active sites, remarkably longer lifetime of charge carriers and adjustable band gap structure, the prepared ultrathin porous CN nanosheets show the enhanced photocatalytic performance for the degradation of methyl orange (MO) under visible light. The degradation efficiency of optimal CN nanosheet photocatalyst for MO is 5.75 times that of bulk CN. This work provides a facile and universal relevance approach to engineer the band structures of CN by introduction of rich C and porous morphology for high-performance photocatalytic, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion. Graphic Abstract

The possibility of the formation of structures such as compounds of elements between chalcogenides and the transition group of metals in the crystal lattice of silicon is studied. This is an urgent problem in electronics. It is shown that, under certain technological conditions, a sufficient concentration of unit cells is formed, which leads to a change in the band structure of silicon itself; i.e., a micro- and nanoscale inclusion in silicon with a direct-gap structure is obtained. The possibilities of creating a fundamentally new class of photocells with an extended spectral sensitivity region, as well as light-emitting devices, light-emitting diodes, and lasers based on them, are shown.

In this paper, we present a number of novel pure-carbon structures generated from cyclo[18]carbon. Due to the very high reactivity of cyclo[18]carbon, it is possible to link these molecules together to form bigger molecular systems. In our studies, we generated new structures containing 18, 36 and 72 carbon atoms. They are of different shapes including ribbons, sheets and tubes. All these new structures were obtained in virtual reactions driven by external forces. For every reaction, the energy requirement was evaluated exactly when the corresponding transition state was found or it was estimated through our new approach. A small HOMO–LUMO gap in these nanostructures indicates easy excitations and the multiple bonds network indicates their high reactivity. Both of these factors suggest that some potential applications of the new nanostructures are as components of therapeutically active carbon quantum dots, terminal fragments of graphene or carbon nanotubes obtained after fracture or growing in situ in catalytic reactions leading to the formation of carbonaceous materials.