Field Penetration Depth Research Articles

The FFLO State in the Dimer Mott Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

The superconducting phase diagram for a quasi-two-dimensional organic superconductor, κ-(BEDT-TTF)2Cu[N(CN)2]Br, was studied using pulsed magnetic field penetration depth measurements under rotating magnetic fields. At low temperatures, Hc2 was abruptly suppressed even by small tilts of the applied fields owing to the orbital pair-breaking effect. In magnetic fields parallel to the conducting plane, the temperature dependence of the upper critical field Hc2 exhibited an upturn and exceeded the Pauli limit field HP in the lower temperature region. Further analyses with the second derivative of the penetration depth showed an anomaly at 31–32 T, which roughly corresponded to HP. The origin of the anomaly should not be related to the orbital effect, but the paramagnetic effect, which is almost isotropic in organic salts, because it barely depends on the field angle. Based on these results, the observed anomaly is most likely due to the transition between the Bardeen-Cooper-Schrieffer (BCS) and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states. Additionally, we discuss the phase diagram and physical parameters of the transition by comparing them with other FFLO candidates.

Design and Fabrication of Fringing Field Capacitive Sensor for Non-Contact Liquid Level Measurement

The capacitive sensors are widely used for liquid level measurement in different applications, but the contact type capacitive sensors suffer from frequent maintenance and drift of the sensor output. The present paper proposes a simple noncontact interdigital (IDT) fringing field capacitance sensor for liquid level measurement. The sensor can be made using flexible /non-flexible substrate, and it can be used to measure the liquid level of the vessel for both planar and non-planar surfaces. Theory of level measurement using the sensor has been discussed. Four different IDT sensor (1-n-1) configurations such as 1-1-1, 1-3-1, 1-5-1 and 1-11-1 have been designed, analysed, simulated (finite element method), and fabricated to measure water and insulating transformer oil levels from 0 to 40 mm. The analytical expressions are derived for 1-n-1 configuration to estimate the value of capacitance and the maximum field penetration depth of the sensors. The capacitance value of all four sensors varies almost linearly with the variation of liquid level. Experimental results show that the sensitivity of the 1-5-1 IDT sensor is 40 fF/mm. Performances of the sensors were compared with other capacitive sensors reported in the literature. The sensor is capable to detect the water level with a resolution of 0.1 mm.

Reflection and absorption of electromagnetic radiation by inhomogeneous photoionized plasma, produced by multiphoton ionization of inert gas atoms.

The interaction of electromagnetic radiation with inhomogeneous plasma formed by multiphoton ionization of inert gas atoms has been studied. In high-frequency and normal skin effects modes the field structure in plasma is described and reflection and absorption coefficients are found. It is shown that as the thickness of the plasma region, in which the photoelectron density grows linearly, increases, both the depth of field penetration and the absorption coefficient increase, too. It is found that, due to the Ramzauer-Townsend effect, there is a relative increase in the effective frequency of photoelectron collisions with atoms, which is accompanied by a significant increase in the absorption coefficient.

Chitosan-Integrated Single-Mode Tapered Optical Fiber DENV II E Protein Sensor

This work reports the enhancement of a single-mode tapered optical fiber (TOF) sensor for Dengue virus (DENV) II E protein using chitosan. Chitosan, an organic nanomaterial with excellent biocompatibility and abundant binding sites, was deposited on TOF as an intermediate layer between the activated taper surface and the anti-DENV II E protein antibodies. The best DENV sensing performance was attained at chitosan thickness of 17.13 nm, which was attributed to the optimum balance between the auxiliary layer thickness and penetration depth of the evanescent field. An enhanced sensitivity value of 14.19 nm/nM was achieved compared to the sensitivity obtained by standard configuration sensor. A lower dissociation constant, K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> of 1.00×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> M was also acquired, which implies a higher affinity towards the targeted E protein. Findings from this work highlight the potential of organic nanomaterial such as chitosan for biosensor enhancement and further emphasize the capability of fiber optic sensors for detection of dengue virus as well as other antigens.

Electronic structure, electron-phonon coupling, and superconductivity in noncentrosymmetric ThCoC2 from ab initio calculations

Superconductors without inversion symmetry in their crystal structure are known to exhibit unconventional properties. Recently, based on the measured temperature dependence of the magnetic field penetration depth, superconductivity in noncentrosymmetric $\mathrm{ThCoC_2}$ was proposed to be a nodal $d$-wave and mediated by the spin fluctuations. Moreover, a non-BCS behavior of the temperature dependence of the electronic specific heat and the magnetic upper critical field were reported. In this work, the electronic structure, phonons and electron-phonon coupling are studied in $\mathrm{ThCoC_2}$ on the basis of \textit{ab initio} computations. The effect of the spin-orbit coupling on the electronic structure and electron-phonon interaction is analyzed, and a large splitting of the electronic band structure is found. The calculated electron-phonon coupling constant $\lambda = 0.59$ remains in decent agreement with the experimental estimates, suggesting that the electron-phonon interaction is strong enough to explain superconductivity with $T_c \simeq 2.5$~K. Nevertheless, we show that the conventional isotropic Eliashberg formalism is unable to describe the thermodynamic properties of the superconducting state, as calculated temperature dependence of the electronic specific heat and magnetic penetration depth deviate from experiments, which is likely driven by the strong spin-orbit coupling and inversion symmetry breaking. In addition, to shed more light on the pairing mechanism, we propose to measure the carbon isotope effect, as our calculations based on the electron-phonon coupling predict the observation of the isotope effect with an exponent $\alpha \simeq 0.15$.

Comprehensive study on glycoprotein detection via polymer fiber sensor decorated with dome-like Ag nanoislands and ZnO nanorods

The surface plasmon resonance (SPR) based polymer fiber sensor is experimentally demonstrated via ZnO/Ag nano-heterostructure bi-layer coating with novel configuration. Glycoprotein detecting criteria is theoretically explained via changing the band gap and refractive index (RI) of ZnO, absorption of leaking light with analyte media, penetration depth of evanescence field, interaction of SPR with evanescence wave, hydrophilicity of ZnO surface and electrochemistry of the ZnO surface. The optical analysis of ZnO(nanorods)/Ag/polymer sample reveals that increasing the glycoprotein concentration, shifts (0.022 eV) the DL emission towards higher wavelength. Electron transferring from donor groups of glycoproteins when interact and bond with ZnO molecules are responsible for this shift. Plasmon resonance shift of Δθ: ~2.21º by increasing the glycoprotein dose from 0 to 0.209 ppm illustrates, interaction of SPR with evanescence wave. Sensitivity of developed polymer fiber sensor is calculated via analysis of output emission spectra and the maximum value achieved are 21 dB/ppm and 45.9 nm/ppm for intensity and wavelength respectively, having the minimum detection limit of 0.021 ppm. Our accurate designed fiber sensor can open up a new opportunity towards application in chemical and biological industries.

Influence of spatial winding distribution of flexible eddy current sensor on quantitative monitoring of subsurface cracks

This paper proposes a flexible eddy current sensor based on TMR sensor. Firstly, the influence of three kinds of sensors with different spatial winding distributions on the penetration depth of magnetic field is analyzed through theoretical derivation. Then, the finite element model is established to analyze the eddy current distribution on the cross-section of the specimen under different excitation frequency and spatial winding distribution. The distribution of eddy current can be improved by increasing the spatial winding distribution. Finally, the corresponding sensors are prepared for subsurface crack monitoring. The experimental results show that the sensor with a spatial winding distribution of 10 mm can quantitatively monitor the cracks below 3 mm of material surface, and increasing the space winding distribution of the sensor to 20 mm, it can quantitatively monitor cracks below 5 mm of material surface, and the crack monitoring accuracy is consistent with the spacing between excitation lines.

Polytetrafluoroethylene Films in Rigid Polyurethane Foams' Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor.

As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation field into PTFE and PUR foams is determined experimentally. Experiments are made in order to evaluate the difference between measurements on single PUR foams’ samples and on complex samples “PUR foams + PTFE film” with two calibration modes. A modification factor and a small modification criterion are defined and values of modifications are estimated in numerical calculations. Conclusions about possible practical applications of PTFE films in dielectric permittivity measurements of rigid PUR foams with one-side access capacitive sensor are made.

How Geometry Affects Sensitivity of a Differential Transformer for Contactless Characterization of Liquids

The electrical and dielectric properties of liquids can be used for sensing. Specific applications, e.g., the continuous in-line monitoring of blood conductivity as a measure of the sodium concentration during dialysis treatment, require contactless measuring methods to avoid any contamination of the medium. The differential transformer is one promising approach for such applications, since its principle is based on a contactless, magnetically induced conductivity measurement. The objective of this work is to investigate the impact of the geometric parameters of the sample or medium under test on the sensitivity and the noise of the differential transformer to derive design rules for an optimized setup. By fundamental investigations, an equation for the field penetration depth of a differential transformer is derived. Furthermore, it is found that increasing height and radius of the medium is accompanied by an enhancement in sensitivity and precision.

A wavelet approach for the variable-order fractional model of ultra-short pulsed laser therapy

In this paper, the ultra-short pulsed laser treatment is numerically simulated for a focused laser beam applied to a cylindrical domain. To do so, the general form of the variable-order fractional-order, dual-phase lag bioheat transfer equation is implemented. To determine the major affecting parameters, the dimensionless form of the heat equation is derived and solved numerically. An efficient method based on the 2D Legendre wavelets is developed to provide a numerical solution for this variable-order time fractional model. The man advantage of the proposed algorithm is that it converts the solution of the problem into solution of a system of algebraic equations. The validity of the formulated method is investigated through one numerical example. The effect of several operational and thermo-physical properties including the phase lag time, fractional order, and the duration of active laser beam in each on/off cycle on the thermal field and heat penetration depth is examined. According to the results, it is concluded that by increasing the fractional order from 0.1 to 0.9, 65.1% increase in the penetration length occurs.

Vertical-junction photodiodes for smaller pixels in retinal prostheses

Objective. To restore central vision in patients with atrophic age-related macular degeneration, we replace the lost photoreceptors with photovoltaic pixels, which convert light into current and stimulate the secondary retinal neurons. Clinical trials demonstrated prosthetic acuity closely matching the sampling limit of the 100 μm pixels, and hence smaller pixels are required for improving visual acuity. However, with smaller flat bipolar pixels, the electric field penetration depth and the photodiode responsivity significantly decrease, making the device inefficient. Smaller pixels may be enabled by (a) increasing the diode responsivity using vertical p–n junctions and (b) directing the electric field in tissue vertically. Here, we demonstrate such novel photodiodes and test the retinal stimulation in a vertical electric field. Approach. Arrays of silicon photodiodes of 55, 40, 30, and 20 μm in width, with vertical p–n junctions, were fabricated. The electric field in the retina was directed vertically using a common return electrode at the edge of the device. Optical and electronic performance of the diodes was characterized in-vitro, and retinal stimulation threshold measured by recording the visually evoked potentials in rats with retinal degeneration. Main results. The photodiodes exhibited sufficiently low dark current (<10 pA) and responsivity at 880 nm wavelength as high as 0.51 A W−1, with 85% internal quantum efficiency, independent of pixel size. Field mapping in saline demonstrated uniformity of the pixel performance in the array. The full-field stimulation threshold was as low as 0.057 mW mm−2 with 10 ms pulses, independent of pixel size. Significance. Photodiodes with vertical p–n junctions demonstrated excellent charge collection efficiency independent of pixel size, down to 20 μm. Vertically oriented electric field provides a stimulation threshold that is independent of pixel size. These results are the first steps in validation of scaling down the photovoltaic pixels for subretinal stimulation.

Low-Temperature Processing of Electronic Materials Using Uniform Microwave Fields

This article presents the recent literature on the unique and surprising capability of microwave energy to effect chemical reactions at lower temperatures. These lower processing temperatures provide improved thermomechanical properties of organic and inorganic material combinations used in microelectronic assemblies. Variable-frequency microwave (VFM) technology eliminates arcing and produces the large and highly uniform fields necessary for use in high-volume manufacturing. Wafer coatings of polyimide thermoplastics can be fully polymerized 100-200°C lower with VFM than with thermal ovens, which lowers stress and warpage. VFM curing of thermoset adhesives for underfill, bonding, and package assembly can be done well below the usually inviolate “ultimate” glass transition temperature without vitrification and in less time. The unique kinetics and thermodynamics of microwave energy produce high chemical reactivity even after the high-viscosity thermoset gelation point. VFM-cured thermosets are highly uniform with less stress and warpage even on large substrates and panels. Field uniformity and penetration depth produce better adhesion and higher fracture strength. The lower process temperatures inherently produce more stable and reliable final products and allow for less costly low-temperature build materials and temperature-sensitive device designs. The anneal and activation process temperatures of implanted ions in silicon can also be reduced by half with VFM, which results in nearly zero dopant diffusion and high-quality SPE regrowth and low numbers of defect sites.

Investigation of the effect of metallization ratio and side shift on the interdigitated electrodes performance for biochemical sensing

This paper investigates the effect of metallization ratio and side shift on the performance of interdigitated electrodes (IDEs). The IDEs were modelled using normal mesh and adaptive mesh refinement techniques to investigate the modelling error. The performance parameters such as electric field distribution, crosstalk and penetration depth of IDEs and the phenomenon of impedance biosensor based on surface conductivity model was simulated using COMSOL Multiphysics software. A detailed analysis was carried out to see the effect of metallization ratio on these performance parameters. In the simulation, the metallization ratio of IDEs was varied between 0.2–0.9, and the variation in side shift was 1–50 µm. A significant reduction in modelling error was obtained for adaptive mesh refinement (AMR) based IDEs model. The IDEs with metallization ratio 0.7 and side shift between 10–20 µm have shown higher measurement sensitivity. For validation of simulation results, experiments were conducted on fabricated IDEs with different metallization ratios. IDEs with metallization ratios 0.3, 0.5 and 0.7 were fabricated using PCB technology. The impedance spectra were obtained for a 10–100 mM KCl solution using electrochemical impedance spectroscopy (EIS). Through simulation and from experimental results, higher measurement sensitivity from IDEs was obtained at 0.7 metallization ratio. Finally, this paper demonstrates the importance of metallization ratio and side shift to ensure higher measurement sensitivity from IDEs when used for biochemical sensing applications.

Low kinetic inductance superconducting MgB2 nanowires with a 130 ps relaxation time for single-photon detection applications

Properties of superconducting nanowires set the performance level for superconducting nanowire single photon detectors (SNSPDs). Reset time in commonly employed large area SNSPDs, 1–10 ns, is known to be limited by the nanowire’s kinetic inductance to the load impedance ratio. On the other hand, reduction of the kinetic inductance in small area (waveguide integrated) SNSPDs prevents biasing them close to the critical current due to latching into a permanent resistive state. In order to reduce the reset time in SNSPDs, superconducting nanowires with both low kinetic inductance and fast electron energy relaxation are required. In this paper, we report on a study of kinetic inductance in narrow (15–100 nm) and long (up to 120 μm) superconducting MgB2 nanowires made from 5 nm thick films, offering such combination of properties. Such films were grown using hybrid physical chemical vapor deposition, resulting in a critical temperature of ∼32 K, and a switch current density of 5 × 107 A cm−2 (at 4.8 K). Using microwave reflectometry, we measured a kinetic inductance of L k0(4.8 K) = 1.3–1.6 pH/□ regardless of the nanowire width, which results in a magnetic field penetration depth of ∼90 nm. These values are very close to those in pristine MgB2. We showed that after excitations by a 50 fs pulsed laser the reset time in 35 nm × 120 μm MgB2 nanowires is 130 ps, which is more than a factor of 10 shorter than in NbN nanowires of similar length-to-width ratios. Depending on the bias current, such MgB2 nanowires function as single-, double, or triple-photon detectors for both visible (λ = 630 nm) and infrared (λ = 1550 nm) photons, with a dark count rate of <10 cps. Although the apparent photon detection efficiency seems so far to be low, further technological advances (uniform nanowire width, smaller thickness, increasing the switching current closer to the pair-breaking current) may improve this figure of merit.

Theoretical study on the magnetic properties of the superconductor FeSe

Identifying the form of superconducting order parameter is still a controversial problem for the iron-based superconductor FeSe. Based on anisotropic two-component Ginzburg–Landau theory, we study the temperature dependence of upper critical field and London penetration depth for FeSe. Without including the spin paramagnetic effect, all of our theoretical calculations fit the experimental data well in a broad temperature range. Our results thus show that FeSe is a two-gap s-wave superconductor. And the anisotropy of effective masses in the band with larger (or smaller) gap can be estimated as about 10 (or 2) respectively.

Механизм формирования критического тока высокотемпературных сверхпроводников, содержащих сквозные микроскопические дефекты

The critical current of a model high-temperature superconductor (HTSC) with defects in the form of through holes (antidots) with a characteristic size greater than or of the order of the penetration depth of the magnetic field is calculated. To do this, the subprocesses equivalent to the trapping of the magnetic flux by the hole and the creation of a vortex at the edge of the hole are introduced into the model of layered HTSC. It is shown that accounting for these subprocesses leads to the appearance of a physical mechanism that allows us to correctly describe the non-monotonic dependence of the critical current on the characteristic size of the antidot, similar to that observed in the experiment. Calculations were performed for a pure superconductor and a superconductor containing nanoscale pinning centers. It is shown that the presence of nanoscale pinning centers along with antipoints does not change the qualitative picture of the influence of the antidot radius on the pinning character of the magnetic flux and the behavior of the critical current in the HTSC.

Dynamics of magnetic flux penetration into superconductor with power-law current–voltage characteristics

This article examines the penetration of a magnetic field into a high-temperature type-II superconductor that is in a viscous flow regime and in an external magnetic field. Analytical formulas are obtained for the depth and rate of the magnetic field penetration into the superconductor as a function of the problem parameters, particularly the exponent n that characterizes the rate of vortex penetration into the superconducting half-space.

Grating-Coupled Surface Plasmon-Polariton Sensing at a Flat Metal-Analyte Interface in a Hybrid-Configuration.

Surface plasmon resonance-based sensors have emerged as commercially fostering portable biodetectors. The scientific community is engaged in extensive research to improve their performance in terms of sensitivity, selectivity, and reproducibility for the recognition of specific biomolecules. Essentially, there is a need for miniaturizing the size of existing sensors with innovative designs without compromising their bioaffinity and sensitivity performance. In this work, we propose and demonstrate a grating-coupled surface plasmon polariton (SPP) sensor on a thin flat gold layer using a hybrid configuration. The proof of concept of the grating architecture has been realized through an innovative fabrication procedure, with experimental verification of its bulk sensitivity. The geometry is identical to the prism-coupling configuration, yet with miniaturization and compactness. Characteristics of the excited modes in the spectral regime of interest are investigated using the finite-difference time-domain simulations. The effective index calculation of the resonance conditions and the accompanying field distribution can identify the excited SPP and metal-assisted guided-mode resonance modes. Detailed probing of the electric field distribution of the desired SPP mode reveals an extended evanescent decay length of 1284 nm, close to the theoretical limit, and an extended propagation length of 270 μm. The experimental demonstration of the reflectance dip with two different analyte media perceived an increased bulk sensitivity of 1133 nm/RIU. Remarkably, this resonant mode exhibits sensing capabilities for a wide range of analyte refractive indexes. We believe that the fabricated configuration with observed high sensitivity and calculated ultradeep evanescent field penetration depth along with extended propagation length can lead to the designing of a hands-on biochip for detecting large biomolecules.

Multifrequency Inductive Sensor System for Classification of Bimetallic Coins

The reliable classification of coin sets from different countries and counterfeit coins is an essential means of securing cash circulation. Especially bimetallic coins, such as 2-Euro coins, are often subjected to counterfeit by mixing them with coins of other countries or by imitations. In this article, a real-time embedded sensor system is proposed, based on inductance spectroscopy to characterize and identify bimetallic coins having similar geometric properties and looking similar at a first view. The system is based on inductance spectroscopy varying the penetration depth of the magnetic field in the bimetallic structure of the coin, which generally contains buried layers of other metals. The experimental evaluation shows that the bimetallic coins from different countries can be identified and classified by the use of the support vector machine, a machine learning algorithm. Experimental results showed that the system reached a classification accuracy up to 100% within a response rate of 36.62 ms per five bimetallic coins.

Suppression of the s-Wave Order Parameter Near the Surface of the Infinite-Layer Electron-Doped Cuprate Superconductor Sr0.9La0.1CuO2

The temperature dependencies of the in-plane (λab) and out-of-plane (λc) components of the magnetic field penetration depth were investigated near the surface and in the bulk of the electron-doped superconductor Sr0.9La0.1CuO2 by means of magnetization measurements. The measured λab(T) and λc(T) were analyzed in terms of a two-gap model with mixed s+d-wave symmetry of the order parameter. λab(T) is well described by an almost pure anisotropic d-wave symmetry component (≃96%), mainly reflecting the surface properties of the sample. In contrast, λc(T) exhibits a mixed s+d-wave order parameter with a substantial s-wave component of more than 50%. The comparison of λab−2(T) measured near the surface with that determined in the bulk by means of the muon-spin rotation/relaxation technique demonstrates that the suppression of the s-wave component of the order parameter near the surface is associated with a reduction of the superfluid density by more than a factor of two.