Iron diffusivity into superconducting YBa2Cu3O7−δ at oxygen-assisted sintering: structural,magnetic, and transport properties

Optimization of materials exhibiting high-temperature superconductivity for producing controllable nano-devices is crucial for industrial applications. Herein we report a comprehensive study of the diffusion process between YBa₂Cu₃O_7−δ (YBCO) and iron particles. Fe diffusion into the YBCO matrix could be fundamental for multilayer systems with YBCO/Fe-alloy interfaces. We have found that the orthorhombic YBCO structure adopts to 3 wt% Fe, while for higher Fe content, a formation of BaFeO_3−δ and iron oxides was observed. Complementary measurements confirmed the strong superconductivity suppression in YBCO-Fe materials containing more than 7 wt% Fe. The YBCO with diffused Fe material retain the unit cell orthorhombicity (max. 3 wt% Fe), and their superconducting properties follow the principle of critical scaling with different exponents (γ). The critical current density (J_c), pinning fields (H_P) exhibit γ = 1, the first critical field (H_c1) shows γ = 1/2, and critical temperature (T_c) demonstrates γ = 7/4.     

Terahertz narrow bandstop, broad bandpass filter using double-layer S-shaped metamaterials

Abstract In this study, double-layer S-shaped metamaterials （MMs） are analyzed by terahertz time-domain spectroscopy. These materials exhibit narrow bandstop and broad bandpass transmission properties at both horizontal and vertical electric-field polarizations. A 117% increase in the unloaded quality factor is experimen- tally observed for these materials. The center frequency is approximately 0.45 THz, with a 3-dB bandwidth of 0.52 THz from 0.20 to 0.72 THz at normal incidence. The measured average insertion loss is 0.5 dB with a ripple of 1 dB. These results show that double-layer S-shaped MMs are effective in designing tunable terahertz devices.     

Terahertz detectors based on superconducting hot electron bolometers

Low noise terahertz(THz)heterodyne detectors based on superconducting niobium nitride(NbN) hot electron bolometers(HEBs)have been studied.The HEB consists of a planar antenna and an NbN bridge connecting across the antenna’s inner terminals on a high-resistivity Si substrate.The double sideband noise temperatures at 4.2 K without corrections have been characterized from 0.65 to 3.1 THz.The excess quantum noise factor β of about 4 has been obtained,which agrees well with the calculated value.Allan variance of the HEB has been measured,and Allan time up to 20 s is obtained using a microwave feedback method.Also,the intermediate frequency gain bandwidth(GBW)was measured using two dierent methods,resulting in same GBW value of about 3.5 GHz.     

Josephson Plasmon Resonance in Tl2Ba2CaCu2O8 High-Temperature Superconductor Tunable Terahertz Metamaterials

The Josephson plasmon resonance (JPR) offers a valuable probe to investigate the superconductivity in layered cuprate superconductors. However, the coupling between free space radiation and JPR in high-temperature superconductor (HTS) film remains challenging because the excitation of JPR demands the c-axis oriented electric field. The subwavelength resonators in metamaterials can enhance the localized electric field, which can be utilized to resolve this difficulty. Here, a tunable terahertz (THz) metamaterial made from Tl₂Ba₂CaCu₂O₈ (Tl-2212) HTS film is developed. The spectral response of Tl-2212 metamaterial has a tunable property at temperatures up to 90 K. The resonant excitation of Josephson plasmon in the metamaterial is observed. Simulation results indicate that the scattering of subwavelength resonators can provide the component of the z-axis electric field for the resonant excitation. The coupling between JPR and resonance modes of metamaterials is observed and explained using coupled mode theory. The temperature dependence of JPR frequency shows accordance with the experimental results of the pure film. This work provides an avenue to excite the JPR and probe superconducting condensate in the layered superconductor. The development of Josephson plasmonic metamaterials may contribute to tunable and nonlinear THz devices.     

A single-photon fault-detection method for nanocircuits that use GaN material

As the complexity of nanocircuits continues to increase,developing tests for them becomes more difficult.Failure analysis and the localization of internal test points within nanocircuits are already more difficult than for conventional integrated circuits.In this paper,a new method of testing for faults in nanocircuits is presented that uses single-photon detection to locate failed components(or failed signal lines)by utilizing the infrared photon emission characteristics of circuits.The emitted photons,which can carry information about circuit structure,can aid the understanding of circuit properties and locating faults.In this paper,in order to enhance the strength of emitted photons from circuit components,test vectors are designed for circuits’components or signal lines.These test vectors can cause components to produce signal transitions or switching behaviors according to their positions,thereby increasing the strength of the emitted photons.A multiple-valued decision diagram(MDD),in the form of a directed acrylic graph,is used to produce the test vectors.After an MDD corresponding to a circuit is constructed,the test vectors are generated by searching for specific paths in the MDD of that circuit.Experimental results show that many types of faults such as stuck-at faults,bridging faults,crosstalk faults,and others,can be detected with this method.     

A demonstration of half-metallicity in graphene using Mn3O4 nanosheet

The recent prediction of the edge modification by a magnetic impurity spin to create half-metallicity in a graphene sheet is demonstrated. Ultrafine Mn₃O₄ sheets of size 10 nm are grown on graphene to observe the remarkable effect of half-metallicity with a 90% change in magnetoresistance at room temperature. The demonstration of a huge negative magnetoresistance using a magnetic impurity spin will make graphene a potential candidate for spintronic devices.     

High-yield solvothermal synthesis of single-crystalline tin oxide tetragonal prism nanorods

The tetragonal prism SnO₂ nanorods with the rutile structure have been successfully synthesized by a simple solvothermal method from high concentration precursors without any surfactant. Their sizes, morphologies and structure were studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), select-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The SnO₂ nanorods obtained by the solvothermal method exhibit higher crystalline quality and better dispersion compared with the samples prepared by the hydrothermal method. Our results suggest that the solvent plays an important role to obtain high-yield SnO₂ nanorods with high quality.     

Temperature-Controlled Optical Activity and Negative Refractive Index

Chiral media exhibit optical activity, which manifests itself as differential retardation and attenuation of circularly polarized electromagnetic waves of opposite handedness. This effect can be described by different refractive indices for left- and right-handed waves and yields a negative index in extreme cases. Here, active control of chirality, optical activity, and refractive index is demonstrated. These phenomena are observed in a terahertz metamaterial based on 3D-chiral metallic resonators and achiral vanadium dioxide inclusions. The chiral structure exhibits pronounced optical activity and a negative refractive index at room temperature when vanadium dioxide is in its insulating phase. Upon heating, the insulator-to-metal phase transition of vanadium dioxide effectively renders the structure achiral, resulting in absence of optical activity and a positive refractive index. The origin of the structure's chiral response is traced to magnetic coupling between front and back of the structure, whereas the temperature-controlled chiral-to-achiral transition is found to correspond to a transition from magnetic to electric dipole excitations. The use of a fourfold rotationally symmetric design avoids linear birefringence and dichroism, allowing such a structure to operate as tunable polarization rotator, adjustable linear polarization converter, and switchable circular polarizer.     

超导磁通量子比特中的共振隧穿现象

在20mK的低温下,在由Nb/AlOx/Nb结构成的磁通量子比特样品上,通过初态的制备,成功观测到了双势阱中的共振隧穿现象。这一现象在不同的势垒高度下,都得到了证实。通过对共振峰随时间演化的测量,发现其演化受到隧穿概率与分布概率的影响。