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Optical Properties of Planar and Annular Ternary Superconducting Photonic Crystals in Near-Zero-Permittivity Operation Range
摘要： Optical properties of ternary superconducting planar/annular photonic crystals composed of a high-temperature superconductor and two dielectrics were theoretically investigated based on transfer matrix methods in Cartesian and cylindrical coordinates. Electrodynamics of superconductor were modelled using two-fluid model. It is of interest to observe that, for a planar structure, there exists an additional high reflectance band termed as superpolariton gap near the superconducting threshold wavelength for the TM wave at oblique incidences and some reflection dips also were found in the TM reflectance. However, the superpolariton gap and reflection dips were seen for an annular geometry at higher order azimuthal number. For an annular structure, the size of superpolariton gap can be controlled by simply adjusting the starting radius. Moreover, the superpolariton gap in both structures strongly depends on the operating temperature, different combinations of dielectric refractive indices, and thicknesses of dielectric materials.
关键词： Annular,Superconductor,Photonic crystal,Superpolariton
更新于2025-09-19 17:15:36
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Molecular beam epitaxy of superconducting PdTe2 films on topological insulator Bi2Te3
摘要： Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, high-quality superconducting PdTe2 films are deposited on the topological insulator Bi2Te3 surface using molecular beam epitaxy. The surface topography and electronic properties of PdTe2/Bi2Te3 heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form PdTe2 film on Bi2Te3 surface rather than diffuse into Bi2Te3. The superconductivity of the PdTe2/Bi2Te3 heterostructure is detected at a transition temperature of ~1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions.
关键词： superconductor,heterostructure,molecular beam epitaxy,topological insulator
更新于2025-09-19 17:15:36
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Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires
摘要： Semiconductor-superconductor hybrid systems have outstanding potential for emerging high performance nanoelectronics and quantum devices. However, critical to their successful application is the fabrication of high quality and reproducible semiconductor-superconductor interfaces. Here, we realize and measure axial Al-Ge-Al nanowire heterostructures with atomically precise interfaces, enwrapped by an ultra-thin epitaxial Si layer further denoted as Al-Ge/Si-Al nanowire heterostructures. The heterostructures were synthesized by a thermally induced exchange reaction of single-crystalline Ge/Si core/shell nanowires and lithographically defined Al contact pads. Applying this heterostructure formation scheme enables self-aligned quasi one-dimensional crystalline Al leads contacting ultra-scaled Ge/Si segments with contact transparencies greater than 96%. Integration into back-gated field-effect devices and continuous scaling beyond lithographic limitations allows us to exploit the full potential of the highly transparent contacts to the 1D hole gas at the Ge-Si interface. This leads to the observation of ballistic transport as well as quantum confinement effects up to temperatures of 150 K. Low temperature measurements reveal proximity-induced superconductivity in the Ge/Si core/shell nanowires. The realization of a Josephson field-effect transistor allows us to study the sub-gap structure caused by multiple Andreev reflections. Most importantly, the absence of a quantum dot regime indicates a hard superconducting gap originating from the highly transparent contacts to the 1D hole-gas, which is potentially interesting for the study of Majorana zero modes. Moreover, underlining the importance of the proposed thermally induced Al-Ge/Si-Al heterostructure formation technique, our system could contribute to the development of key components of quantum computing such as gatemon or transmon qubits.
关键词： 1D hole gas,hard superconducting gap,transparent contacts,superconductor-semiconductor hybrids,nanowire heterostructure,germanium
更新于2025-09-12 10:27:22
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Weyl points in systems of multiple semiconductor-superconductor quantum dots
摘要： As an analogy to the Weyl point in k-space, we search for energy levels which close at a single point as a function of a three-dimensional parameter space. Such points are topologically protected in the sense that any perturbation which acts on the two-level subsystem can be corrected by tuning the control parameters. We find that parameter-controlled Weyl points are ubiquitous in semiconductor-superconductor quantum dots and that they are deeply related to Majorana zero modes. In this paper, we present several semiconductor-superconductor quantum-dot devices which host parameter-controlled Weyl points. Furthermore, we show how these points can be observed experimentally via conductance measurements.
关键词： semiconductor-superconductor quantum dots,conductance measurements,Majorana zero modes,Weyl points
更新于2025-09-11 14:15:04
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Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors
摘要： The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 X 104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.
关键词： Solution Blow Spinning,nano-Y2BaCuO5,nano-whiskers,Bulk YBCO,High temperature superconductor,Single-grain superconductor,YBa2Cu3O7-x
更新于2025-09-10 09:29:36
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Slot Lens Antenna Based on Thin Nb Films for the Wideband Josephson Terahertz Oscillator
摘要： An oscillator based on the distributed tunnel superconductor-insulator-superconductor junction with an ultrawide operating bandwidth of up to 100% of the central frequency seems to be a promising type of directional source of continuous electromagnetic radiation in the terahertz frequency range. In this paper, we propose a scheme of a terahertz oscillator integrated on a single microchip with a transmitting lens antenna with the slot structure in a 200-nm Nb film to radiate the signal into the open space. We also proposed and numerically simulated several designs of a planar slot antenna matched (in the input) with a Josephson oscillator and (in the output) with a silicon elliptical lens. The obtained results of the matching of the oscillator output power with the antenna of various designs operating in four frequency ranges: 250–410, 330–570, 380–520, and 420–700 GHz are presented. The antenna beam patterns and impedances are calculated as well.
关键词： terahertz,superconductor,slot antenna,oscillator,Josephson junction
更新于2025-09-10 09:29:36
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Structural, elastic, electronic, thermodynamic, and optical properties of layered BaPd2As2 pnictide superconductor: A first principles investigation
摘要： BaPd2As2, belonging to the 122 pnictide group, is an iron-free layered transition metal arsenide which exhibits superconductivity at low temperature when realized in the ThCr2Si2 type structure (I4/mmm). We have performed density functional theory (DFT) based calculations to investigate the structural, elastic, electronic, thermodynamic, and optical properties of BaPd2As2 in this study. The structural, elastic, and the band structure features are compared with the available experimental and theoretical results. Pressure and temperature dependences of various important thermodynamic functions, e.g., bulk modulus, specific heats at constant pressure and volume, coefficient of volume thermal expansion, and Debye temperature are studied in details for the first time. The optical parameters of BaPd2As2 are also studied in details for the first time. The optical properties compliment the electronic band structure characteristics. Optical constants show significant dependence of the state of polarization of the incident electric field. BaPd2As2 exhibits high reflectance in the infrared and near-visible region and strongly absorbs the ultraviolet radiation. The relevance of the electronic energy density of states and the characteristic phonon frequency to superconductivity in BaPd2As2 is also discussed.
关键词： BaPd2As2 superconductor,Density functional theory,Electronic band structure,Optical properties,Elastic constants,Thermodynamic properties
更新于2025-09-10 09:29:36
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Tuning of the defect mode in a 1D superconductor-semiconductor crystal with hydrostatic pressure dependent frequency of the transverse optical phonons
摘要： This study aims to investigate a transmittance spectrum in a one-dimensional photonic crystal, which is surrounded by air and composed of alternating layers of a superconductor (HgBa2Ca2Cu3O8+δ) and a semiconductor (GaAs), using the transfer matrix and two-fluid models. Herein, we considered the pressure-dependence of the superconductor’s critical temperature and the pressure-dependence, in the semiconductor, in both the angular frequency of the transverse optical phonons and the thickness of layers. Initially, we found that increasing the pressure for fixed thickness values of the superconductor results in a shift in the larger frequencies of the transmittance spectrum and the photonic band gaps. With an increase in the thickness of the superconductor layer at a fixed pressure and thickness values of the semiconductor, an increase in the width of the photonic band gaps was observed. When a defective GaAs semiconductor layer was inserted into the structure due to the dissipative features of the semi-conductor, a defective mode with a transmittance of less than 1.0 was found inside the photonic band gaps. When the thickness of the superconductor layer was increased, while keeping the pressure and thickness of the semiconductor constant, the defect mode shifted to shorter frequencies. It was also found that the shift and the number of defective modes in the photonic band gaps increase when the thickness of the defective semiconductor layer increases.
关键词： superconductor,transfer-matrix method,semiconductor,defect mode,Photonic crystal
更新于2025-09-10 09:29:36
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[SpringerBriefs in Materials] Anisotropic Metal Chalcogenide Nanomaterials (Synthesis, Assembly, and Applications) || Applications
摘要： Interest in anisotropic 1D and 2D nanostructures has been steadily increasing due to their large surface area, quantum con?nement effect, and superior optoelectrical or thermoelectrical properties. Anisotropic geometry and size reduction comparable to the Debye length can alter the optical, electric, and magnetic properties of the bulk counterparts. Focusing on MCs prepared in solution the major interests for practical applications are thermoelectric power phases, generation or electronic device cooling, high performance electrodes for batteries, nanocrystal-based photovoltaic devices, and photodetectors. Recently, new potential uses of the solution-based MC nanocrystals are being investigated, which include localized surface plasmon resonance (LSPR) and oxygen reduction reaction (ORR). MC thin ?lms prepared by the vacuum process have shown the possibilities as new class of materials such as topological insulator, semiconductor with a high electron mobility, and superconductor. Although the organic surfactants indispensable in solution chemistry diminish such superior physical properties, solution-based approach has large room to achieve such physical properties. This chapter will introduce recent advances in the practical applications of the anisotropic MC nanocrystals, and introduce brie?y the potential applications.
关键词： thermoelectric,oxygen reduction reaction,photodetector,metal chalcogenides,localized surface plasmon resonance,photovoltaic,superconductor,topological insulator,anisotropic nanostructures
更新于2025-09-04 15:30:14