Investigating the Omnidirectional Photonic Band Gap in One-Dimensional Superconductor–Dielectric Photonic Crystals with a Modified Ternary Fibonacci Quasiperiodic Structure

In this paper, an omnidirectional photonic band gap (OBG) of one-dimensional (1D) superconductor–dielectric photonic crystals (SDPCs) with a modified ternary Fibonacci quasiperiodic structure which originates from Bragg gap is theoretically investigated by the transfer matrix method (TMM) in detail. The SDPCs are composed of superconductor and two kinds of homogeneous, isotropic dielectric. Such OBG is independent of the incidence angle and the polarization of electromagnetic wave (EM wave). From the numerical results, the OBG can be notably enlarged by tuning the thickness of superconductor and dielectric layers but cease to change with increasing the Fibonacci order. The OBG also can be manipulated by the ambient temperature of system. Especially, the ambient temperature of system is close to the critical temperature. However, the damping coefficient of superconductor has no effects on the OBG. The gap/midgap ratio of OBG also is studied by those parameters. It is shown that 1D SDPCs with a modified ternary Fibonacci quasiperiodic structure have a superior feature in the enhancement of OBG compared with the conventional 1D ternary and conventional ternary Fibonacci quasiperiodic SDPCs.     

Omnidirectional Photonic Band Gap in One-Dimensional Ternary Superconductor-Dielectric Photonic Crystals Based on a New Thue–Morse Aperiodic Structure

In this paper, an omnidirectional photonic band gap (OBG) of one-dimensional (1D) ternary superconductor-dielectric photonic crystals (SDPCs) based on a new Thue–Mores aperiodic structure is theoretically studied by the transfer matrix method (TMM) in detail. Compared to zero- $\bar{n}$ gap or single negative (negative permittivity or negative permeability) gap, such OBG originates from Bragg gap. From the numerical results, the bandwidth and central frequency of OBG can be notably enlarged by manipulating the thicknesses of superconductor and dielectric layers but cease to change with increasing the Thue–Mores order. The OBG also can be tuned by the ambient temperature of the system especially close to the critical temperature. However, the damping coefficient of the superconductor layer has no effects on the OBG. The relative bandwidth of OBG also is investigated by the parameters as mentioned above. It is clear that such 1D ternary SDPCs have a superior feature in the enhancement of the bandwidth of OBG compared to the conventional ternary SDPCs and conventional ternary Thue–Mores aperiodic SDPCs. These results may provide theoretical instructions to design the future SDPCs devices.     

Broadening of Photonic Band Gap in a One—Dimensional Superconductor Star Waveguide Structure

The present paper describes the theoretical investigation of enlarged reflection bands (photonic band gaps) in a 1D star waveguide (SWG) structure consists of superconductor and dielectric as its constituent materials. For the present study, we take the different combinations of superconductor and dielectric materials as a backbone and side branches of the SWG structure. In order to obtain the dispersion relation, Interface Response Theory (IRT) has been employed. Photonic band gaps of SWG structure having superconductor?Csuperconductor, superconductor?Cdielectric, and dielectric?Csuperconductor materials are compared with the band gaps of the conventional photonic crystal (PC) structure having superconductor?Csuperconductor and dielectric?Csuperconductor materials. Analysis of the dispersion characteristics shows that there exists no band gaps for conventional PC when both layers are made of the same superconducting materials (as the usual case) while the SWG structure shows forbidden bands of finite width even the backbone and side branches are made of same materials. Also, the SWG structure having superconductor?Cdielectric shows the wider reflection bands in comparison with the structure having dielectric?Csuperconductor as its constituent materials, while for the conventional PC structure it is same in both the cases. Further, the effect of temperature and the effect of variation of number of grafted branches on the photonic bands of SWG structure have been studied.     

Angle- and Thickness-Dependent Photonic Band Structure in?a?Superconducting Photonic Crystal

The angle- and thickness-dependent photonic band structures in a one-dimensional superconducting photonic crystal are theoretically investigated based on the transfer matrix method. The band structure is studied near and below the threshold frequency at which the superconducting material has a zero permittivity. The gap structure is analyzed as a function of the thicknesses of the two constituent superconducting and dielectric materials. In the angular dependence of the band structure, it is found that in the TM-polarization there exists a strongly localized superpolariton gap in the vicinity of the threshold frequency. This gap is shown to be enhanced as the angle increases.     

Large Increase of the Critical Field in a Magnet–Superconductor Nanowire Hybrid

We have fabricated two-dimensional periodic arrays of parallel magnetic and superconducting nanowires on a silicon substrate. Parallel magnetic (nickel) nanowires of cross section 90 nm by 300 nm form a periodic array with Pb₈₂Bi₁₈ superconducting nanowires of cross section 200 nm by 100 nm. These nanostructures were characterized with Scanning Electron Microscopy (SEM) and magnetic properties were studied with Magnetic Force Microscopy (MFM). The phase diagram was determined by electrical transport measurements. Depending on the temperature, the second critical field was 2 to 3 times larger than that of a homogeneous Pb₈₂Bi₁₈ superconducting control film. The superconducting phase diagram and transport properties exhibit strong hysteresis in a magnetic field. Results are explained on the basis of the theory of magnet–superconductor hybrids.     

Ginzburg–Landau Study of Superconductor with Regular Pinning Array

The vortex distributions and dynamics in superconductors with triangular and honeycomb pinning arrays are investigated by numerical simulation of the two- dimensional (2-D) time-dependent Ginzburg–Landau equations. Periodic boundary conditions are implemented through specific gauge transformations under lattice translations. We model the pinning sites as holes. The simulation results at different magnetic fields are presented. For film with regular triangular pinning array, the vortices are all captured within the holes for a wide range of magnetic fields. For film with regular honeycomb pinning array, the interstitial vortices appear at relatively low magnetic fields. With an increase of magnetic field, the new vortices may enter the holes again and keep the number of vortices at the interstitial positions unchanged. These results confirm our explanations of the experimental results we obtained earlier.     

Dielectric characteristics of ore minerals in a 10–40 GHz frequency range

A new approach to investigation of the complex dielectric permittivity of both nonmetallic and ore minerals in the microwave frequency range is proposed. Using this approach, data on the complex permittivity of sphalerite, magnetite, and labradorite in a 10–40 GHz frequency range have been obtained for the first time. A method is proposed for calculating the complex permittivity from experimentally measured frequency dependences of the reflection and transmission coefficients of a plane-parallel plate of a given mineral. Approximate expressions that can be used for calculations of the complex refractive index and permittivity of minerals are presented.     

Scattering of Electromagnetic Waves by a Reflector Antenna with Feed Containing a Nonlinear Metal–Dielectric–Metal Contact

We have studied scattering of electromagnetic waves by a reflector antenna with feed containing a metal–dielectric–metal contact with nonlinear voltage–current characteristic. We propose and evaluate the effectiveness of ways to eliminate stray radiation.     

Parametric Amplification of Magnetoacoustic Oscillations in a Ferromagnet–Piezoelectric Structure

Technical Physics Letters - A parametric amplification of magnetoacoustic oscillations in a disk resonator containing a FeBSiC ferromagnetic layer and a lead zirconate–titanate piezoelectric...     

Self-Consistent Theory of Transport in Quasi–One-Dimensional Superconducting Wires

We study superconducting transport in quasi–one-dimensional homogeneous wires in the cases of both equilibrium and nonequilibrium quasiparticle populations, using the quasiclassical Green's function technique. We consider superconductors with arbitrary current densities and impurity concentrations ranging from the clean to the dirty limit. Local current conservation is guaranteed by ensuring that the order parameter satisfies the self-consistency equation at each point. For equilibrium transport, we compute the current, the order parameter amplitude, and the quasiparticle density of states as a function of the superfluid velocity, temperature, and disorder strength. Nonequilibrium is characterized by incoming quasiparticles with different chemical potentials at each -end of the superconductor. We calculate the profiles of the electrostratic potential, order parameter, and effective quasiparticle gap. We find that a transport regime of current-induced gapless superconductivity can be achieved in clean superconductors, the stability of this state being enhanced by nonequilibrium.     

Quantum Phases and Collective Excitations of a Spin-Orbit-Coupled Bose–Einstein Condensate in a One-Dimensional Optical Lattice

The ground state of a spin-orbit-coupled Bose gas in a one-dimensional optical lattice is known to exhibit a mixed regime, where the condensate wave function is given by a superposition of multiple Bloch-wave components, and an unmixed one, in which the atoms occupy a single Bloch state. The unmixed regime features two unpolarized Bloch-wave phases, having quasimomentum at the center or at the edge of the first Brillouin zone, and a polarized Bloch-wave phase at intermediate quasimomenta. By calculating the critical values of the Raman coupling and of the lattice strength at the transitions among the various phases, we show the existence of a tricritical point where the mixed, the polarized and the edge-quasimomentum phases meet, and whose appearance is a consequence of the spin-dependent interaction. Furthermore, we evaluate the excitation spectrum in the unmixed regime and we characterize the behavior of the phonon and the roton modes, pointing out the instabilities occurring when a phase transition is approached.     

Refrigeration of separate,user-supplied payloads with Normal–Insulator–Superconductor tunnel junctions

Normal metal–Insulator–Superconductor (NIS) tunnel junctions can be used to selectively remove the hottest electrons in the normal metal, thereby causing it to cool. NIS tunnel junctions have already been used to cool lithographically integrated payloads [1], but this requires integration of two disparate fabrication processes. To increase the flexibility of NIS refrigerators, we have designed a stage cooler based on NIS tunnel junctions that will be able to cool arbitrary, user-supplied payloads from 300 mK to 100 mK. This stage cooler can be backed by a helium-3 refrigerator to provide a lightweight and simple means of reaching 100 mK in space applications. In this paper, we describe the design of our stage cooler and present calculations of the cooling power and time required to reach 100 mK.     

Dielectric behavior of polyaniline–CNTs composite in microwave region

Films of polyaniline (PANI) and polyaniline–CNTs composites have been synthesized by solution casting technique. Fourier transform infrared spectroscopic studies of PANI and PANI–CNTs composite films indicated the presence of interaction between CNTs and molecular chains of PANI. Dielectric properties of PANI and composite films have been investigated in the frequency range of 8.0–12.0 GHz. The real part of permittivity (ε′) and loss factor (tan δ) were found to be higher in PANI–CNTs composite films as compared to the PANI film. The increasing behavior of ε′ and tan δ has been attributed to the interaction present between CNTs and PANI molecular chains and increase of conductivity of PANI films after incorporation of CNTs.     

Characterization of Dielectric Properties in Liquid–Solid Phase Transition

A method for determining the complex dielectric permeability of liquids based on the temperature changes in geometrical parameters (thickness) of samples and over the phase transition range is proposed. Allowing the measurements to be made in a wide temperature range (–190 to 60°C) at different frequencies (0.1–100 kHz), this technique is used for establishing the complex dielectric permeability of ethanol as a function of temperature. The accuracy of coincidence of the obtained values with the data reported in the literature is 3%.     

Structure and orientation relationship of new precipitates in a Cu–Cr–Zr alloy

The crystallography and morphology of the nano-sized precipitate particles in a ternary Cu–Cr–Zr alloy were studied by transmission electron microscopy. A new type of face-centred-cubic (f.c.c) Cr-rich precipitate was observed. This precipitate is ordered and solute enriched on alternate {110} f.c.c planes, with an ellipsoid-shaped morphology. The new orientation relationship (OR) between the precipitate and Cu matrix satisfies [211]M//[011]p and [100]M//[111]p, {-111}M//{200}p and {02-2}M//{02-2}p. The difference between this new OR and the Nishiyama–Wasserman OR between body-centred-cubic (b.c.c) Cr and the Cu matrix can be detailed by Δg vectors in the diffraction patterns. Furthermore, the precipitation strengthening effect is increased greatly with the formation of these new precipitate particles when compared to binary Cu–Cr alloys.     

Momentum Distribution in a One-Dimensional Bose–Hubbard Model at Incommensurate Fillings

We study the momentum distribution of the hard-core extended Bose–Hubbard model at incommensurate fillings in one dimension. From the finite-size scaling behavior of the zero-momentum occupancy, the Luttinger liquid parameters are obtained as a function of interaction strength and filling. The curvature of the momentum distribution shows distinction between the easy-plane and the easy-axis region, and the occupancy at the zone boundary indicates the filling fraction.     

Transient Behavior of Photoconductivity in Ge–Si Single Crystals

The transient behavior of photoconductivity in single crystals of Ge–Si solid solutions was studied. The parameters of sticking and recombination centers were determined. The results suggest that impurity agglomerates and silicon precipitates act as recombination and sticking centers, respectively.     

On the Structure of the Superfluid State and Quasiparticle Spectrum in a Bose Liquid with a Suppressed Bose–Einstein Condensate

A self-consistent model of the superfluid (SF) state of a Bose liquid with strong interaction between bosons and a weak single-particle Bose–Einstein condensate (BEC) is considered. The ratio of the BEC density n ₀ to the total particle density n of the Bose liquid is used as a small parameter of the model, n ₀/n?1, unlike in the Bogolyubov theory of a quasi-ideal Bose gas, in which the small parameter is the ratio of the number of supracondensate excitations to the number of particles in an intensive BEC, (n?n ₀)/n ₀?1. A closed system of nonlinear integral equations for the normal ~Σ₁₁(p, ω) and anomalous ~Σ₁₂(p, ω) self-energy parts is obtained with account for terms of first order in the BEC density. A renormalized perturbation theory is used, which is built on combined hydrodynamic (at p→0) and field (at p≠0) variables with analytic functions ~Σ _ij (p, ε) at pε0 and ε→0 and a nonzero SF order parameter ~Σ₁₂(0, 0)≠0, proportional to the density ρ _s of the SF component. Various pair interaction potentials U(r) with inflection points in the radial dependence and with an oscillating sign-changing momentum dependence of the Fourier component V(p) are considered. Collective many-body effects of renormalization (“screening”) of the initial interaction, which are described by the bosonic polarization operator Π(p, ω), lead to a suppression of the repulsion [V(p)<0] and an enhancement of the effective attraction [V(p)<0] in the respective domains of nonzero momentum transfer, due to the negative sign of the real part of Π(p, ω) on the “mass shell” ω=E(p). In the framework of the “soft spheres” model with the single fitting parameter—the value of the repulsion potential at r=0—the quasiparticle spectrum E(p) is calculated, which is in good accordance with the experimental spectrum E _exp(p) of elementary excitations in superfluid ⁴He. It is shown that the roton minimum in the quasiparticle spectrum is directly associated with the first negative minimum of the Fourier component of the renormalized (“screened”) potential of pair interaction between bosons.