Junction Model Research Articles

A closer look at the Nernst-Planck model for liquid junctions in galvanic cells and the concept of EMF

It is realized now that what is called the liquid-junction potential is given, in the classical theory of Nernst and Planck, by a line integral, which is path independent only in the case of a single independent concentration. Although previous model studies suggest that this integral is consistent with the potential calculated by the 1D version of Poisson's equation in the limit of long diffusion times, it is shown here, with a simple static model, that this may be true in the 3D space only at an infinitely large cross-section of the junction. At finite cross-sections, supposing that a charge separation exists, the potential difference across it is a function of the area of the cross-section and the distance across it, which is at variance with the properties of the integral. It is argued therefore that this integral cannot be interpreted in terms of electrostatics, but represents a quantity, the EMF, which is conceptually different from the potential.

The steady-state Archard adhesive wear problem revisited based on the phase field approach to fracture

The problem of adhesive wear is herein investigated in relation to periodic asperity junction models in the framework of the Archard interpretation suggesting that wear debris formation is the result of asperity fracture. To this aim, the phase field model for fracture is exploited to simulate the crack pattern leading to debris formation in the asperity junction model. Based on dimensional analysis considerations, the effect of the size of the junction length, the lateral size of the asperity, and the amplitude of the re-entrant corner angles $$\gamma $$ and $$\beta $$ defined by the junction geometry is examined in the parametric analysis. Results show that two failure modes are expected to occur, one with a crack nucleated at the re-entrant corner $$\gamma $$ , and another with a crack nucleated at the re-entrant corner $$\beta $$ , depending on the dominant power of the stress-singularity at the two re-entrant corner tips. Steady-state adhesive wear, where the initial asperity junction geometry is reproduced after debris formation, is observed for asperity junctions with $$\gamma = 45^\circ $$ , almost independently of the lateral size of the asperity and of the horizontal projection of the junction length.

Plasmonic photocapacitance of self-assembled gold colloidal nanoparticle monolayers

We report on the plasmo-electronic properties of self-assembled monolayers of gold colloidal nanoparticles (NPs) formed on a polyimide flexible substrate. The dependence of both resistance and capacitance of these NP assemblies on temperature, bias voltage, optical excitation, and strain is investigated both experimentally and theoretically. Resistance and capacitance appear to bring complementary information on the charge transport properties of the NP assemblies as they exhibit opposite behaviors. Based on a nanocircuit junction model combined with numerical simulations, we were able to account for both the resistance and capacitance and their photo-induced modifications. The dependence of the capacitance on laser irradiation intensity and wavelength was measured, and the role of the surface plasmon resonance was pointed out. We show that the plasmonic-induced photocapacitance can reach 43% for a moderate irradiation intensity of 3.5W/cm2. Moreover, the NP assemblies, deposited on flexible substrate, were submitted to a uniaxial strain which allows for controlling the interparticle distances and hence for probing the plasmo-electro-mechanical properties of the assembly. We found that, under plasmonic pumping of charges, the photo-capacitance gauge factor is three times larger than the one measured under dark conditions, in agreement with the calculations. The presented work thus paves the way to the emergence of a new class of plasmonic-enhanced capacitance strain sensors.

Josephson coupling in the dissipative state of a thermally hysteretic μ -SQUID

Micron-sized superconducting interference devices ($\mu$-SQUIDs) based on constrictions optimized for minimizing thermal runaway are shown to exhibit voltage oscillations with applied magnetic flux despite their hysteretic behavior. We explain this remarkable feature by a significant supercurrent contribution surviving deep into the resistive state, due to efficient heat evacuation. A resistively shunted junction model, complemented by a thermal balance determining the amplitude of the critical current, describes well all experimental observations, including the flux modulation of the (dynamic) retrapping current and voltage by introducing a single dimensionless parameter. Thus hysteretic $\mu$-SQUIDs can be operated in the voltage read-out mode with a faster response. The quantitative modeling of this regime incorporating both heating and phase dynamics paves the way for further optimization of $\mu$-SQUIDs for nano-magnetism.

Hysteresis from nonlinear dynamics of Majorana modes in topological Josephson junctions

We reveal that topological Josephson junctions provide a natural platform for the interplay between the Josephson effect and the Landau-Zener effect through a two-level system formed by coupled Majorana modes. We build a quantum resistively shunted junction (RSJ) model by modifying the standard textbook RSJ model to take account of the two-level system from the Majorana modes at the junction. We show that the dynamics of the two-level system is governed by a nonlinear Schr\"odinger equation and solve the equations analytically via a mapping to a classical dynamical problem. This nonlinear dynamics leads to hysteresis in the I-V characteristics, which can give a quantitative explanation to recent experiments. We also predict the coexistence of two interference patterns with periods $h/e$ and $h/2e$ in topological superconducting quantum interference devices.

Spontaneous and Controlled Chaos Synchronization in Intrinsic Josephson Junctions

Synchronization properties of model systems containing large numbers of phase oscillators have many potential biophysical and other applications. Biophysical examples include networks of pacemaker cells in the heart and suprachiasmatic nucleus of the brain. In physical systems, the phase dynamics of high- $T_{\rm c}$ superconducting materials continue to attract attention, since systems of intrinsic Josephson junctions form natural arrays of coupled phase oscillators. As such, they have the potential to act as systems in which various exotic synchronization effects may be observed. In this paper, we make a more detailed exploration of the parameter space containing regions of spontaneous chaos synchronization in the CCJJ + DC model of intrinsic Josephson junctions. Extensive regions of phase synchronization—corresponding to the Shapiro steps with zero charge density in the S-layers—are found through numerical simulation. By computing the Lyapunov exponent spectra, we see that the spontaneous chaos synchronization occurs within certain subregions that overlap with uncharged steps in the IV-characteristics. We tried to stabilize the spontaneous chaos synchronization over a wider range of parameters, by applying a global, noninvasive, and proportional control scheme. The control is affected by applying a time-dependent phase shift to the external electromagnetic radiation, proportional to the total voltage. The effect of the control is found to be three-fold. First, it tends to broaden the current interval over which lower harmonic Shapiro steps occur. Second, it does not change the width in the current range over which the chaos synchronization occurs. Third, it makes the chaos synchronization more robust to thermal noise. The chaos synchronization we report here may be useful in any applications requiring more powerful, high-frequency, and chaotic signals, such as in secure communication.

Electrical Сharacteristics of Long Josephson Junctions Based on Tungsten Nanorods as Weak Links: Effect of Random Critical-Current Distributions

The numerical model of long Josephson junctions with Gaussian spread of critical currents has been developed. The model allowed calculating the IV-characteristics and power of emission of long junctions. Zero-field steps in IV-characteristics in the hysteretic region were found. When the spread of critical currents was comparable with the value of the averaged critical current, particularities corresponded to zero-field steps were found in the derivative of the IV-characteristic far above the hysteretic region. Results were qualitatively explained in ranges of the existing theory of zero-field steps in IV-curves of Josephson junctions with random distributions of critical currents. The model was applied for the approximation of particularities in the derivative of the earlier measured IV-curve of the heterostructure consisted of two superconducting electrodes made up of molybdenum-rhenium alloy and a hybrid semiconductor tunnel barrier with a nanosized silicon layer which contained tungsten nanoclusters [the MoRe-Si(W)-MoRe heterostructure]. The model described adequately positions of particularities in the derivative of the IV-characteristic in the wide range of voltages.

Highly Responsive, Polarization Sensitive, Self-Biased Single GeO2-Ge Nanowire Device for Broadband and Low Power Photodetectors

Highly uniform and dense GeO2 nanowires with Ge as the core were grown on Si (001) substrates by vapor–liquid–solid technique with an aim to utilize GeO2 as the active material for photodetectors. X-ray photoelectron spectroscopy was carried out to investigate the composition and interfaces of the resultant Ge/GeO2 NWs. The observed broad and visible photoluminescence emission from as-grown core–shell NW heterostructure is attributed to oxygen-related defect states in the GeO2 shells. Single Ge-GeO2 NW based metal–semiconductor–metal photodetectors were fabricated using nanolithography techniques. Self-driven (zero bias) detectors have been found to be responsive to a broadband spectrum from 350 to 900 nm with a peak responsivity (∼0.6 × 104 A/W) and detectivity (∼3.8 × 1012 Jones). The high gain in photocurrent has been explained using a back-to-back metal–semiconductor junction model in single NW. The device also shows sensitivity to polarization-dependence of light source. Finite element method (FEM) b...

Effect of the depletion region in topological insulator heterostructures for ambipolar field-effect transistors

Formation of a depletion region at the vertically stacked topological insulator $p\text{\ensuremath{-}}n$ heterostructures is one of the effective approaches to minimize residual carrier density in the bulk regions. Here, we report on characterization of field-effect transistor (FET) based on ${(\mathrm{B}{\mathrm{i}}_{0.26}\mathrm{S}{\mathrm{b}}_{0.74})}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ topological insulator heterostructures with a vertical $p\text{\ensuremath{-}}n$ junction configuration. The thicknesses of the top $p\text{\ensuremath{-}}{(\mathrm{B}{\mathrm{i}}_{0.26}\mathrm{S}{\mathrm{b}}_{0.74})}_{2}\mathrm{S}{\mathrm{e}}_{3}$ layer vary from $d=8$ to 25 nm with 3-nm constant thickness of the bottom $n\text{\ensuremath{-}}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. Even at zero gate voltage, increasing thickness of the top layer inverts the dominant conducting carrier from $n$-type to $p$-type. With applying gate voltage, the effect of depletion region at the interface is clearly revealed as a voltage shift of charge neutral point in ambipolar FET operation. The systematic shift of charge neutral point in FET operation clearly indicates that the formation of depletion region can be explained with conventional semiconductor $p\text{\ensuremath{-}}n$ junction model. In the topological insulator $p\text{\ensuremath{-}}n$ heterostructures, the thickness tuning of both $p$-type and $n$-type layers is quite important to minimize the residual charge density in the whole device region. The band engineering with $p\text{\ensuremath{-}}n$ junction will be further applicable to extract the electrical properties of surface state.

Kinetic Schemes in Open Interacting Systems.

We discuss utilization of kinetic schemes for description of open interacting systems, focusing on vibrational energy relaxation for an oscillator coupled to a nonequilibirum electronic bath. Standard kinetic equations with constant rate coefficients are obtained under the assumption of time scale separation between the system and bath, with the bath dynamics much faster than that of the system of interest. This assumption may break down in certain limits, and we show that ignoring this may lead to qualitatively wrong predictions. Connection with more general, nonequilibrium Green's function (NEGF) analysis is demonstrated. Our considerations are illustrated within generic molecular junction models with electron-vibration coupling.

Trajectory Tracking between Josephson Junction and Classical Chaotic System via Iterative Learning Control

This article addresses trajectory tracking between two non-identical systems with chaotic properties. To study trajectory tracking, we used the Rossler chaotic and resistive-capacitive-inductance shunted Josephson junction (RCLs-JJ) model in a similar phase space. In order to achieve goal tracking, two stages were required to approximate target tracking. The first stage utilizes the active control technique to transfer the output signal from the RCLs-JJ system into a quasi-Rossler system. Next, the RCLs-JJ system employs the proposed iterative learning control scheme in which the control signals are from the drive system to trace the trajectory of the Rossler system. The numerical results demonstrate the validity of the proposed method and the tracking system is asymptotically stable.

Spin-Torque-Biased Magnetic Strip: Nonequilibrium Phase Diagram and Relation to Long Josephson Junctions.

Spin-torque-biased magnetic dynamics in an easy-plane ferromagnet (EPF) is theoretically studied in the presence of a weak in-plane anisotropy. While this anisotropy spoils U(1) symmetry, thereby quenching the conventional spin superfluidity, we show that the system instead realizes a close analog of a long Josephson junction (LJJ) model. The traditional magnetic-field and electric-current controls of the latter map, respectively, onto the symmetric and antisymmetric combinations of the out-of-plane spin torques applied at the ends of the magnetic strip. This suggests an alternative route towards realizations of superfluidlike transport phenomena in insulating magnetic systems. We study a spin-torque-biased phase diagram, providing an analytical solution for static multidomain phases in the EPF. We adapt an existing self-consistency method for the LJJ to develop an approximate solution for the EPF dynamics. The LJJ-EPF mapping has the potential for producing applications with superconductor-based circuit functionality at elevated temperatures. The results apply equally to antiferromagnets with suitable effective free energy in terms of the Néel order instead of in-plane magnetization.

Phonon chirality tuned through interface transmission in a one-dimensional atomic junction model

There has been growing interest in revealing exotic properties of chiral phonons since they were found in honeycomb AB lattice, and very recently they were experimentally verified in a tungsten diselenide monolayer (2018 Science 359 579). In this work, we manipulate phonon chirality through interface transmission via a one-dimensional atomic junction model by using the scattering boundary method. Due to the difference of phase change between two transverse directions induced by the anisotropy at interface coupling, the phonon polarization can be tuned between circular and linear in the high-frequency range. In a double-junction atomic model with an anisotropic center, we find that the phase change accumulates when the phonon transmits through the interface material thus the phonon can be tuned between different chirality in the medium frequency range. The phase change is found to linearly depend on the width of the interface material, while the transmission coefficient vibrates. To obtain the same value of the transmission coefficients along the two transverse directions and thus to keep the outgoing phonon circularly polarized, we can connect two interface materials with opposite anisotropy, where the phase-change difference for chirality tuning can be adjusted by the difference of widths of the two materials. Therefore, by using the atomic junction model, we find that the phonon chirality can be effectively tuned through interfaces, which is helpful for the manipulation and application of chiral phonons.

Multi-indicator Road Traffic State Assessment Based on Path State

In order to evaluate the traffic condition of urban road, the article makes an actual modeling of the urban road junctions and the analysis of the status of sub-lanes. Combined with various impedance factors of the road network, in this paper, a state coefficient matrix is used to represent the road network impedance data, and a road traffic status assessment system based on the actual path status with multi-parameter indexes is proposed. The evaluation system is improved based on the existing state assessment methods and breakthroughs in the assessment mode. In the past, it only estimated the overall traffic condition at the intersection; the evaluation method was more efficient and the evaluation result was more accurate. The actual road network in Shijingshan District is used to verify the results. The results show that the algorithm is effective.

On simulation of local fluxes in molecular junctions.

We present a pedagogical review of the current density simulation in molecular junction models indicating its advantages and deficiencies in analysis of local junction transport characteristics. In particular, we argue that current density is a universal tool which provides more information than traditionally simulated bond currents, especially when discussing inelastic processes. However, current density simulations are sensitive to the choice of basis and electronic structure method. We note that while discussing the local current conservation in junctions, one has to account for the source term caused by the open character of the system and intra-molecular interactions. Our considerations are illustrated with numerical simulations of a benzenedithiol molecular junction.

Construction and applications of the manifestly gauge invariant expressions of the solutions of the cosmological perturbation theory

After giving how to construct the gauge invariant perturbation variable in an arbitrarily high order and in the arbitrary background spacetime, we consider the manifestly gauge invariant theory of the cosmological perturbations in the long wavelength limit with the spatially flat homogeneous isotropic universe being the background spacetime. In the previous paper, the physical laws, such as the evolution equations, the constraint equations and the junction conditions become manifestly gauge invariant, by writing them in terms of only the single time background/scalar like objects defined by our previous paper. In the present paper, by extending our definition of the background/scalar like objects from the single time case to the many time case and by writing the solution of the physical law in the form where many time background/scalar like objects are vanishing, the solutions become the manifestly gauge invariant. We derive the formula changing the bases of the many time background/scalar like objects by which we can change the time slices for many times appearing in the solution including the initial time and the final time. We use this formula to our treatment of the evolution of the several slow rolling scalar fields using the τ function introduced by our previous paper. In the manifestly gauge invariant manner, we discuss the solution of the many step reheating, that is, the reheating with the arbitrarily many energy transfer steps. Using the energy density ρ as the evolution parameter, we discuss how well the junction model in which the energy transfers from the oscillatory scalar field fluid to the radiation fluid are described by the metric junctions approximates the reheating process described by the differential equations with the decay terms. By using the useful parametrization of the many step reheating, we manifestly prove that in the many step reheating system where any initial perturbation of each component does not become extremely large compared with the initial perturbations of the other components, compared with the effects of the prominent fluctuation generation processes the nearest to the present time the effects of all the fluctuations generated by the previous fluctuation generation processes become negligibly small. Therefore it can be concluded that in order to know the first/second order Bardeen parameters at the present time it is sufficient to calculate only the effects of the fluctuation of the scalar field fluid which becomes energetically dominant lastly (the curvaton mechanism) and the fluctuation of the decay parameter by which this scalar field fluid decays into the radiation (the modulated reheating mechanism).

Animal Models of the Neuromuscular Junction, Vitally Informative for Understanding Function and the Molecular Mechanisms of Congenital Myasthenic Syndromes.

The neuromuscular junction is the point of contact between motor nerve and skeletal muscle, its vital role in muscle function is reliant on the precise location and function of many proteins. Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders of neuromuscular transmission with 30 or more implicated proteins. The use of animal models has been instrumental in determining the specific role of many CMS-related proteins. The mouse neuromuscular junction (NMJ) has been extensively studied in animal models of CMS due to its amenability for detailed electrophysiological and histological investigations and relative similarity to human NMJ. As well as their use to determine the precise molecular mechanisms of CMS variants, where an animal model accurately reflects the human phenotype they become useful tools for study of therapeutic interventions. Many of the animal models that have been important in deconvolving the complexities of neuromuscular transmission and revealing the molecular mechanisms of disease are highlighted.

(Invited) Multi-Scale and Multi-Physics Modeling for Advancing Photoelectrochemical and Photocatalytic Material and Device Research

Modelling can efficiently support the choice of the most interesting conceptual design approaches, material choices, and operating conditions for photoelectrochemical and photocatalytic devices. Here, I will discuss modeling of three different ideas for versatile and cheap solar hydrogen and syngas production: i) photocatalytic particle suspended in a solution, ii) semiconductor particle-based photoelectrodes (PEs) fabricated by scalable dipping procedures, and iii) high-temperature approaches to photoelectrochemistry. Modeling of scalable photocatalysis suspensions require understanding of the single particle band energetics and kinetics and coupling it to the heat, mass and charge transport processes in a complete suspension. I will show how we use and couple 1D single particle models and 2D suspension simulations to provide material and design guidance of photocatalytic suspension approaches. Modeling of complicated particle-based PEs, on the other hand, requires full 3D multi-scale device models accounting for the morphological details of the nano-scale and then coupling them through homogenization theory to the macroscopic device model. I will show how we utilized nano-tomography to obtain the exact nano-scale morphology and how this morphology is incorporated into direct pore-level modeling to predict inhomogeneity in the variable fields and corresponding underutilization of parts of the PE. Finally, I will show how we use advanced 2D heat transfer models and detailed 1D junction models for mixed electron and ion conductor interfaces to model and explore high temperature approaches to photoelectrochemistry. I will end with a general outlook on modeling of photo-driven devices.

Reversible magnetic logic gates based on spin wave interference

We propose and develop reversible magnetic logic gates based on spin wave interference. The gates consist of passive elements including spin waveguides, cross-junctions, and phase shifters. Logic 0 and 1 are encoded in the phase of the propagating spin wave (0 or π). There are different possible input-output trajectories for the propagating spin waves, where some of the trajectories contain phase shifters and others do not. In each case, the particular input-output trajectory and the resultant output phase depend on the input phase combination. The redirection takes place in the cross junctions. Two waves coming to a junction in-phase propagate through the junction without reflection. In contrast, two waves coming to a junction out-of-phase are completely reflected back. The process of redirection is illustrated by numerical modeling of a nanometer-scale junction comprising two chains of spins, which operates at zero temperature. We also present experimental data on spin wave redirection in a micrometer-size cross junction made of Y3Fe2(FeO4)3 operating at room temperature. Our results demonstrate a prominent spin wave redirection, where the ratio of the transmitted power between the in-phase and out-of-phase cases exceeds 45 dB at room temperature. Based on these experimental data, we estimate the energy per operation in spin wave reversible logic circuits. The proposed reversible gates may provide a route to magnetic logic circuitry with power dissipation less than kT per operation.

Analysis and Compact Modeling of Magnetic Tunnel Junctions Utilizing Voltage-Controlled Magnetic Anisotropy

A macrospin compact model of a perpendicularly magnetized voltage-controlled magnetic tunnel junction (MTJ) is introduced, for the evaluation of electronic and magnetic characteristics associated with its switching behavior. The voltage-driven precessional switching has been shown to outperform current-driven switching in terms of energy, speed, and bit density. However, to realize the device in embedded system memory applications, developing a compact model for simulating hybrid MTJ/CMOS circuits is necessary. This framework also needs to be compatible with conventional computer-aided circuit design tools and flows. In this paper, the voltage-controlled magnetic anisotropy effect is included as a component of the effective magnetic field in a Landau–Lifshitz–Gilbert (LLG) equation-based model. The compact model is described by Verilog-A, providing a numerical solution for a 3-D magnetization trajectory and the corresponding conductance change of the MTJ. We also include the thermal noise effect in the LLG equation to allow the evaluation of stochastic switching behavior under a wide variety of bias conditions, which can be quantified in terms of write error rate (WER). It is shown that the model allows for optimization of write pulse shape and design considerations to achieve the lowest WER for given MTJ parameters.