Junction Behavior Research Articles

Zeeman-Effect-Induced 0-π Transitions in Ballistic Dirac Semimetal Josephson Junctions.

One of the consequences of Cooper pairs having a finite momentum in the interlayer of a Josephson junction is π-junction behavior. The finite momentum can either be due to an exchange field in ferromagnetic Josephson junctions, or due to the Zeeman effect. Here, we report the observation of Zeeman-effect-induced 0-π transitions in Bi_{1-x}Sb_{x}, three-dimensional Dirac semimetal-based Josephson junctions. The large in-plane g factor allows tuning of the Josephson junctions from 0 to π regimes. This is revealed by measuring a π phase shift in the current-phase relation measured with an asymmetric superconducting quantum interference device (SQUID). Additionally, we directly measure a nonsinusoidal current-phase relation in the asymmetric SQUID, consistent with models for ballistic Josephson transport.

Inactivation of low-temperature-induced numerous defects at the electrode/channel interfaces using ultrathin Al2O3 layers

The high demand for flexible and stretchable electronics has resulted in new bottlenecks on the process design of amorphous oxide thin-film transistors (TFTs) fabricated at ≥300 °C that involves low-temperature processes to accommodate for the use of polymer substrates. Unlike previous studies aiming to achieve better channel properties, our study focuses on the low-temperature effects of electrical contacts at the source/drain electrodes and oxide channel junction. The decrease in the process temperature causes unfavorable evident changes from an almost ohmic (350 °C) to Schottky (200 °C) junction and shows coincident trends with the degradation of TFT performances. Thus, we here propose a creative process design using ultrathin Al2O3 interlayers between the electrode and channel, where they inactivate the role of numerous surface defects existing on the a-IZO channels deposited at low temperatures. The a-IZO TFT with 13 Å Al2O3 optimally exhibits a field effect mobility of 17.3 cm2/Vs in the 200 °C low-temperature annealing process, comparable to that of a-IZO TFT annealed at 350 °C. Similarly, the ultrathin Al2O3 interlayers led to the reduced specific contact resistance and ohmic junction behavior. From capacitance–voltage analyses, we elucidated that they were attributed to the significantly reduced trapping events of the charges by passivating the interface defects.

Ritz method analysis of rectilinear orthotropic composite circular plates undergoing in-plane bending and torsional moments

In this article, the elastic problem of composite circular plates with rectilinear orthotropic characteristics, in case of in-plane bending and torsional moments applied, is resolved. According to classical lamination plate theory, the analysis makes use of the Ritz method along with the principle of virtual displacements, originally combined in order to obtain displacements components. The procedure represents an important step for the setting-up of a spot joint element able to simulate in FE analyses the structural behavior of point junctions applied to composite components. The accuracy of the procedure has been demonstrated comparing analytical results to FE reference analyses.

Simulation study for the current matching optimization in In0.48Ga0.52N/In0.74Ga0.26N dual junction solar cells

Abstract In this paper indium gallium nitride (InGaN) is used to design and optimize a dual junction (DJ) solar cell, which is series-connected via a tunnel diode, with a careful analysis of the current matching between the top and the bottom sub-cells. In particular, a bandgap combination of 1.76eV/1.13eV for an In0.48Ga0.52N/In0.74Ga0.26N structure is adopted and several numerical simulation results are presented. The doping concentration and the base thickness of each sub-cell are considered as fitting parameters in order to determine an accurate current matching condition. The In0.48Ga0.52N-based n++/p++ tunnel junction behavior is also taken into account. A maximum short circuit current density of 19.543 mA/cm2 is obtained for a 1 μm-thick base in both the sub-cells, and a p/n doping ratio of 5 × 1018 cm−3/5 × 1015 cm−3 and 1.9 × 1019 cm−3/1.9 × 1016 cm−3 for the top and the bottom cell, respectively. The optimized DJ solar cell exhibits an open circuit voltage of 1.713 V, a fill factor of 82.49%, and a conversion efficiency of 28.78%. The external quantum efficiency and the current (power) density-voltage characteristics of different devices are investigated in detail.

Atomic rheology of gold nanojunctions.

Despite extensive investigations of dissipation and deformation processes in micro- and nano-sized metallic samples1-7, the mechanisms at play during the deformation of systems with ultimate (molecular) size remain unknown. Although metallic nanojunctions, which are obtained by stretching metallic wires down to the atomic level, are typically used to explore atomic-scale contacts5,8-11, it has not been possible until now to determine the full equilibrium and non-equilibrium rheological flow properties of matter at such scales. Here, by using an atomic-force microscope equipped with a quartz tuning fork, we combine electrical and rheological measurements on ångström-size gold junctions to study the non-linear rheology of this model atomic system. By subjecting the junction to increasing subnanometric deformations we observe a transition from a purely elastic regime to a plastic one, and eventually to a viscous-like fluidized regime, similar to the rheology of soft yielding materials12-14, although orders of magnitude different in length scale. The fluidized state furthermore exhibits capillary attraction, as expected for liquid capillary bridges. This shear fluidization cannot be captured by classical models of friction between atomic planes15,16 and points to an unexpected dissipative behaviour of defect-free metallic junctions at ultimate scales. Atomic rheology is therefore a powerful tool that can be used to probe the structural reorganization of atomic contacts.

One-step ion beam irradiation manufacture of 3D micro/nanopatterned structures in SiC with tunable work functions

The fabrication and design of high-quality three-dimensional (3D) micro/nanostructures are of great importance for the development of new technology. Herein, we report a one-step technique to controllably manufacture 3D micro/nanopatterned structures with tunable work functions in silicon carbide (SiC). The multiscale micro/nanopatterned structures were produced directly by ion beam irradiation-induced swelling with the assistance of masks. The minimum feature size was ∼52 nm and the swelling height could be controlled flexibly from ∼1 to ∼250 nm. The change of work function of the 3D SiC micro/nanostructures could be tuned in the range between 0 and ∼126.6 meV. Distinct rectifying junction behavior was demonstrated between the irradiated and unirradiated zones. The Young's modulus and hardness values of the irradiated zones stabilized at ∼298.1 GPa and ∼24.9 GPa, respectively.

Seismic behavior of slab-structural wall junction of RC building

In high seismic zone regions, slender reinforced concrete structural walls are commonly used in high-rise buildings as a main lateral load resisting element. These walls are very effective in limiting the lateral drift of the building due to their large in-plane stiffness. However, the presence of floor slabs influences the behavior of the shear wall. Also, the current design requirements do not account for the presence of floor slabs. To understand the behavior of wall-slab junctions and address the shortcomings of the current design requirements, the influence of two parameters, namely (a) aspect ratio and (b) longitudinal reinforcement ratio on the behavior is studied numerically. It is observed that the presence of floor slabs at different levels tends to partition the wall into squat wall panels between two consecutive floors. The wall-slab junctions show large stress concentrations arising from the strut action in the squat panels. It is also observed that the floor slabs can get significantly damaged near the wall-slab junction for lower vertical reinforcement ratios in the wall. Thus, the current code-prescribed minimum reinforcement in shear walls is not sufficient and needs to be revisited at for improved performance.

Growth and Nanofabrication of All-Perovskite Superconducting/Ferromagnetic/Superconducting Junctions

We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below {T}_{Curie}sim 160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias ( Vsim 1 –2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5-nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a sim 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current.

Abnormal solute distribution near the eutectic triple point

Most research into the formation of the lamellar eutectics has focused on the growth patterns. However, those growth patterns can be attributed to the behavior of the triple junction, at which the solute distribution determines the long-range spatial periodicity of patterns. From both theoretical validation and phase-field simulations, we characterize the solute concentration at the triple point and demonstrate the existence of abnormal solute distribution. The solute concentration at the triple point equals the eutectic concentration only when the coexisting solid phases are evenly distributed, which is essential to balance the concentration gradient and maintain the interfacial thermodynamic equilibrium.

Anti-resonance features of destructive quantum interference in single-molecule thiophene junctions achieved by electrochemical gating.

Controlling the electrical conductance and in particular the occurrence of quantum interference in single-molecule junctions through gating effects has potential for the realization of high-performance functional molecular devices. In this work we used an electrochemically gated, mechanically controllable break junction technique to tune the electronic behaviour of thiophene-based molecular junctions that show destructive quantum interference features. By varying the voltage applied to the electrochemical gate at room temperature, we reached a conductance minimum that provides direct evidence of charge transport controlled by an anti-resonance arising from destructive quantum interference. Our molecular system enables conductance tuning close to two orders of magnitude within the non-faradaic potential region, which is significantly higher than that achieved with molecules not showing destructive quantum interference. Our experimental results, interpreted using quantum transport theory, demonstrate that electrochemical gating is a promising strategy for obtaining improved in situ control over the electrical performance of interference-based molecular devices.

Anomalous Diffusion of Endoplasmic Reticulum Constituents

Diffusion of macromolecules and higher-order structures in the crowded interior of cells frequently shows an anomalous behavior with the mean-square displacement (MSD) increasing nonlinearly in time, MSD∝tα. Here we have probed to which extent also larger organelle structures show such an anomalous diffusion and how non-equilibrium contributions affect their diffusional motion [Phys. Rev. E 98, 012406 (2018), in press: Biophys. J. 115 (2018)]. In particular, we have employed single-particle tracking to monitor the motion of tubular junctions in the endoplasmic reticulum (ER) network and of long-lived membrane domains on the ER, called ER exit sites (ERES). Our results show that both, ER junctions and ERES show a distinct anomalous diffusion with a significant anti-correlation of successive step increments that is reminiscent of fractional Brownian motion. Disrupting the microtubule cytoskeleton significantly altered the subdiffusive characteristics of both entities, highlighting that even anomalous diffusion is an actively driven process in living cells. While the diffusion behavior of ER junctions was seen to be directly dependent on the presence and activity of microtubules, ERES were only indirectly affected. ERES therefore can be seen as mobile membrane domains that perform a quasi-one-dimensional random walk on the shivering ER backbone.

Anomalous Low-Temperature Enhancement of Supercurrent in Topological-Insulator Nanoribbon Josephson Junctions: Evidence for Low-Energy Andreev Bound States.

We report anomalous enhancement of the critical current at low temperatures in gate-tunable Josephson junctions made from topological insulator BiSbTeSe_{2} nanoribbons with superconducting Nb electrodes. In contrast to conventional junctions, as a function of the decreasing temperature T, the increasing critical current I_{c} exhibits a sharp upturn at a temperature T_{*} around 20% of the junction critical temperature for several different samples and various gate voltages. The I_{c} vs T demonstrates a short junction behavior for T>T_{*}, but crosses over to a long junction behavior for T<T_{*} with an exponential T dependence I_{c}∝exp(-k_{B}T/δ), where k_{B} is the Boltzmann constant. The extracted characteristic energy scale δ is found to be an order of magnitude smaller than the induced superconducting gap of the junction. We attribute the long-junction behavior with such a small δ to low-energy Andreev bound states arising from winding of the electronic wave function around the circumference of the topological insulator nanoribbon.

Cyclic virtual test on wood furniture by Monte Carlo simulation: from compression behavior to connection modeling

Prediction of durability of wood product is a major challenge and an important goal for furniture industry. Numerical simulation based on approximation methods such as the finite element method (FEM) is an efficient and powerful tool to address this challenge while avoiding expensive experimental testing campaigns. Nevertheless, the strong heterogeneity of wood-based materials, the specific geometrical characteristics of wood-based structures (such as furniture that can often be represented as an assembly of beams, plates and/or shells) and the complex nonlinear 3D local behavior near the connections between structural parts may induce some difficulties in the numerical modeling and virtual testing of furniture for robust design purposes. Especially, when cyclic loading occurs, the behavior of junctions in furniture involves a local permanent strain that increases with the number of cycles and that can lead to an important gap potentially affecting the structural integrity of furniture. In this paper, we present an experimental campaign of cyclic compression tests carried out on spruce specimens. Theses specimens are cut out from a bunk bed and loaded under cyclic compression. The cyclic compression loading applied to the specimens leads to an evolution of the permanent strain during cycles that is modeled using a simple law describing the displacement gap as a function of the number of cycles. Considering the strong dispersion in the mechanical properties of wood-based materials and the variabilities induced by the experimental configuration, a stochastic modeling of the gap is proposed by having recourse to the maximum entropy (MaxEnt) principle in order to take into account the random uncertainties on the experimental setup and between the test specimens. The random mechanical response of a complex corner junction in a bunk bed under cyclic loading is then numerically simulated by using a Monte Carlo numerical simulation method as stochastic solver. This provides independent realizations of the random gap evolution (with respect to the number of cycles) in the bunk bed corner, allowing probabilistic quantities of interest related to the random gap, such as first- and second-order statistical moments (mean value, standard deviation) as well as confidence regions (with a given probability level), to be estimated.

The Behavior Analysis of Magnetoresistive Tunnel Junction Devices in State Space

The behavior of magnetoresistive tunnel junction (MTJ) devices in the electronic (digital) circuits is governed by several differential equations. The LLG equation determines the dynamic of the magnetic polarization vector which ultimately affects the (anti)parallel resistance of MTJs. This vector differential equation is decomposed into two scalar differential equations. In the proposed method, the differential equations are expressed in the state space and the corresponding well-developed theories are applied. In fact, the device is considered as a multi-input multi-output control system and the qualitative solutions are presented. The state diagram gives an insight into the device behavior. It can provide additional information about the device performance and can be considered as a complementary technique of other available analysis approaches. With this ability, the designer can engineer the MTJ devices for their optimum performance in the circuit. Using this theory, we also suggested a power and performance improving approach for the spin transfer torque MTJ-based logic circuits. To show the efficiencies offered by the proposed method, a STT-MRAM cell and an array are designed and it is shown that better specifications can be achieved in terms of switching time and power dissipation. The reliability issues are also investigated and we show that the proposed power/performance improvement approach can effectively consider the reliability concerns.

A classical picture of subnanometer junctions: an atomistic Drude approach to nanoplasmonics.

The description of optical properties of subnanometer junctions is particularly challenging. Purely classical approaches fail, because the quantum nature of electrons needs to be considered. Here we report on a novel classical fully atomistic approach, ωFQ, based on the Drude model for conduction in metals, classical electrostatics and quantum tunneling. We show that ωFQ is able to reproduce the plasmonic behavior of complex metal subnanometer junctions with quantitative fidelity to full ab initio calculations. Besides the practical potentialities of our approach for large scale nanoplasmonic simulations, we show that a classical approach, in which the atomistic discretization of matter is properly accounted for, can accurately describe the nanoplasmonics phenomena dominated by quantum effects.

New sagittal classification of AIS: validation by 3D characterization.

In order to improve surgical planning of sagittal correction in AIS, we proposed a new sagittal classification-Abelin-Genevois et al. Eur Spine J (27(9):2192-2202, 2018. https://doi.org/10.1007/s00586-018-5613-1 ). The main criticism is related to the fact that 2D lateral view results from the projection of the 3D deformity. The aim of this study is to show that the new sagittal classification system is a reliable system to describe the different sagittal scenarios that AIS could create both in 2D and 3D. We performed retrospective radiograph analysis of prospectively collected data from 93 consecutive AIS patients who underwent an examination of the whole spine using the EOS® imaging system. 2D (Keops®) and 3D analyses (sterEOS®) provided frontal and sagittal spinal and spinopelvic parameters. In addition, 3D analysis provided apical vertebra rotation (AVR). Comparing 2D and 3D measurements for the general cohort, excellent correlation can be found for all parameters, but only fairly good for T10L2 and L1S1 angles. The highest variability was observed for T10L2, differences between 2D and 3D measurements being greater when the Cobb angle increased. AVR did not influence concordance between 2D and 3D measurements. Eighty-two percent were similarly classified in 2D and 3D according to the new classification. Misclassified patients were all AIS sagittal type 3 in 3D analysis, thoracolumbar junction (TLJ) lordosis being underestimated on 2D view. In conclusion, for the majority of cases (82%), 2D analysis may provide enough information for decision making when using a semi-automated 2D measurement system. However, in severe cases, especially when Cobb angle exceeds 55°, 3D analysis should be used to get a more accurate view on the thoracolumbar junction behavior. These slides can be retrieved under Electronic Supplementary Material.

Variation-Resilient True Random Number Generators Based on Multiple STT-MTJs

In the Internet of Things era, security concerns may require a cryptography system in every connected device. True random number generators (TRNGs) are preferred instead of pseudorandom number generators in the cryptography systems to achieve a higher level of security. For on-chip applications, we seek scalable and CMOS-compatible devices and designs for TRNGs. In this paper, the stochastic behavior of the spin transfer torque magnetic tunnel junction (STT-MTJ) is utilized for the source of randomness. However, variations and correlations exist in MTJs due to fabrication limitations, so TRNG designs based on a single MTJ have to be postprocessed or tracked in real time to ensure an acceptable level of randomness. Two novel designs are proposed in this paper, which can produce random sequences with high variation resilience. The first design uses a parallel structure to minimize variation effects, and the second design leverages the symmetry of an MTJ pair to take advantage of any correlations. Moreover, a universal circuit for quality improvement is proposed and it can be used with any random number generator. All of the designs are validated in a 28-nm CMOS process by Monte Carlo simulation with a compact model of the MTJ. The National Institute of Standards and Technology (NIST) statistical test suite is used to test the randomness quality of the generated sequences under the scenario of encryption keys in the transport layer security or secure sockets layer (TLS/SSL) cryptographic protocol.

Electrodynamics of Josephson junctions containing strong ferromagnets

Triplet supercurrents in multilayer ferromagnetic Josephson junctions with misaligned magnetization can penetrate thicker ferromagnetic barriers compared to the singlet component. Although the static properties of these junctions have been extensively studied, the dynamic characteristics remain largely unexplored. Here we report a comprehensive electrodynamic characterization of multilayer ferromagnetic Josephson junctions composed of Co and Ho. By measuring the temperature-dependent current-voltage characteristics and the switching current distributions down to 0.3 K, we show that phase dynamics of junctions with triplet supercurrents exhibits long (in terms of proximity) junction behavior and moderately damped dynamics with renormalized capacitance and resistance. This unconventional behavior possibly provides a different way to dynamically detect triplets. Our results show new theoretical models are required to fully understand the phase dynamics of triplet Josephson junctions for applications in superconducting spintronics.

Carbon Nanotube Porins in Amphiphilic Block Copolymers as Fully Synthetic Mimics of Biological Membranes

Biological membranes provide a fascinating example of a separation system that is multifunctional, tunable, precise, and efficient. Biomimetic membranes, which mimic the architecture of cellular membranes, have the potential to deliver significant improvements in specificity and permeability. Here, a fully synthetic biomimetic membrane is reported that incorporates ultra-efficient 1.5 nm diameter carbon nanotube porin (CNTPs) channels in a block-copolymer matrix. It is demonstrated that CNTPs maintain high proton and water permeability in these membranes. CNTPs can also mimic the behavior of biological gap junctions by forming bridges between vesicular compartments that allow transport of small molecules.

DEHP toxicity on vision, neuromuscular junction, and courtship behaviors of Drosophila

Bis(2-ethylhexyl) phthalate (DEHP) is the most common plasticizer. Previous studies have shown DEHP treatment accelerates neurological degeneration, suggesting that DEHP may impact retinal sensitivity to light, neurotransmission, and copulation behaviors. Although its neurotoxicity and antifertility properties have been studied, whether DEHP exposure disrupts vision and how DEHP influences neuromuscular junction (NMJ) have not been reported yet. Moreover, the impact of DEHP on insect courtship behavior is still elusive. Fruit flies (Drosophila melanogaster) were treated with series concentrations of DEHP and observed for lifespan, motor function, electroretinogram (ERG), electrophysiology of neuromuscular junction (NMJ), courtship behaviors, and relevant gene expression. Our results confirmed the DEHP toxicity on lifespan and capacity of motor function and updated its effect on copulation behaviors. Additionally, we report for the first time that DEHP exposure may harm vision by affecting the synaptic signaling between the photoreceptor and the laminar neurons. Further, DEHP treatment altered both spontaneous and evoked neurotransmission properties. Noteworthy, the effect of DEHP exposure on the copulation behavior is sex-dependent, and we proposed potential mechanisms for future investigation.