Parallel Junction Research Articles

Spectral Signatures of Nontrivial Topology in a Superconducting Circuit

Topology, like symmetry, is a fundamental concept in understanding general properties of physical systems. In condensed matter, nontrivial topology may manifest itself as singular features in the energy spectrum or the quantization of electrical properties such as conductance and magnetic flux. Using microwave spectroscopy, we determine that a superconducting circuit with three Josephson tunnel junctions in parallel can possess degeneracies indicative of nontrivial topology. We identify three topological invariants, one of which is related to a hidden quantum mechanical supersymmetry. Measurements show that devices fabricated in different topological regimes fall on a simple phase diagram, which should be robust to junction imperfections and geometric inductance. Josephson tunnel junction circuits, which are readily fabricated with conventional microlithography techniques, allow access to a wide range of topological systems that may have no condensed matter analog. Notable spectral features of these circuits, such as degeneracies and flat bands, may find use in quantum information, sensing, and metrology. Published by the American Physical Society 2024

Spin and orbital Yu-Shiba-Rusinov states and delocalization control of magnetic order in parallel double quantum dot Josephson junctions

Spin and orbital Yu-Shiba-Rusinov states and delocalization control of magnetic order in parallel double quantum dot Josephson junctions

Noise Scaling in SQUID Arrays

Abstract We numerically investigate the noise scaling in high-T_c commensurate 1D and 2D SQUID arrays. We show that the voltage noise spectral density in 1D arrays violates the scaling rule of ~1/N_p for the number N_p of Josephson junctions in parallel. In contrast, in 2D arrays with N_s 1D arrays in series, the voltage noise spectral density follows more closely the expected scaling behaviour of ~N_s/N_p. Additionally, we reveal how the flux and magnetic field rms noise spectral densities deviate from their expected ~(N_sN_p)^{-1/2} scaling and discuss their implications for designing low noise magnetometers.

Half-integer Shapiro steps in MgB2 focused He ion beam Josephson junctions

Abstract Half-integer microwave induced steps (Shapiro steps) have been observed in many different Josephson junction systems, which have attracted a lot of attention because they signify the deviation of current phase relation (CPR) and uncover many unconventional physical properties. In this article, we first report the discovery of half-integer Shapiro steps in MgB2 focused He ion beam (He-FIB) Josephson junctions. The half-integer steps’ dependence on microwave frequency, temperature, microwave power, and magnetic field is also analyzed. We find that the existence of half-integer steps can be controlled by the magnetic field periodically, which is similar to that of high temperature superconductor (HTS) grain boundary junctions, and the similarity of the microstructures between gain boundary junctions and He-FIB junctions is discussed. As a consequence, we mainly attribute the physical origin of half-integer steps in MgB2 He-FIB junctions to the model that a He-FIB junction is analogous to a parallel junctions’ array. Our results show that He-FIB technology is a promising platform for researching CPR in junctions made of different superconductors.

Development of a steady state electrothermal cosimulation model of SiC power modules

Silicon carbide power modules are suitable for high temperature, high voltage and high frequency applications. High operating temperature and high power density bring enormous challenges in chip parallel connection and junction temperature predicting. In this work, a steady state electrothermal cosimulation model is established based on Matlab electrical model and ANSYS thermal analysis model. An experimental study is conducted using a customized single die SiC module. The experimental and numerical results exhibit great agreement, with deviation consistently below 4 %. Then, comprehensive research is conducted to investigate the electrothermal performance of several dies in parallel configuration. The findings unequivocally validate the efficacy of the proposed model in accurately capturing the intricate electrical and thermal characteristics. The proposed numerical model offers a reliable and accurate electrothermal modeling approach for SiC power modules.

Impact of Current on the Parallel Resistance and Junction Capacitance of Light-Emitting Diodes

Impact of Current on the Parallel Resistance and Junction Capacitance of Light-Emitting Diodes

Tuning the supercurrent distribution in parallel ballistic graphene Josephson junctions

Tuning the supercurrent distribution in parallel ballistic graphene Josephson junctions

GaN-Based Ultraviolet Phototransistor With Two Parallel Polarization-Doped Junctions and an Al0.20Ga0.80N Insertion Layer to Achieve Low Dark Current and High Detectivity

GaN-Based Ultraviolet Phototransistor With Two Parallel Polarization-Doped Junctions and an Al_0.20Ga_0.80N Insertion Layer to Achieve Low Dark Current and High Detectivity

The effect of bias current configuration on the performance of SQUID arrays

Designing superconducting electronic devices involves a careful study of all the elements in the circuit, including the superconducting bias leads. In this work, we introduce a theoretical model for two-dimensional (2D) superconducting quantum interference device (SQUID) arrays capable of simulating the voltage-to-magnetic flux response of devices with different bias current configurations. First, we compare uniformly biased and centre biased SQUID arrays by investigating the voltage versus magnetic flux response, maximum transfer function and voltage modulation depth. Then, we calculate the time-averaged fluxoid distributions for one-dimensional (1D) and 2D centre biased arrays. Finally, we study the performance of the two bias current configurations depending on array size, screening parameter, thermal noise strength and kinetic self-inductance fraction. Our calculations reveal: (i) centre biased 1D parallel SQUID arrays present an unusual voltage response caused by the asymmetric fluxoid distribution; (ii) the optimal transfer function of centre biased arrays strongly depends on the number of junctions in parallel; (iii) the performance of centre biased arrays approaches the uniform biased ones when the number of junctions in series exceeds those in parallel; (iv) while the screening parameter and the thermal noise strength clearly affect the device performance, the kinetic to self-inductance fraction seems to play only a secondary role.

Numerical Study of SQUID Array Responses Due to Asymmetric Junction Parameters

Superconducting quantum interference device arrays have been extensively studied for their high magnetic field sensitivity. The performance of these devices strongly depends on the characteristic parameters of their Josephson junctions, i.e. their critical currents and shunt resistances. Using a resistively shunted junction model and including thermal noise, we perform a numerical investigation of the effects of asymmetric Josephson junctions by independently studying variations in the critical currents and junction resistances. We compare the voltage response of a dc-SQUID with a 1D parallel SQUID array and study the maximum transfer function dependence on the number of junctions in parallel, the screening parameter and thermal noise strength. Our results show that the maximum transfer function and linearity increase with the number of junctions in parallel for arrays with different junction resistances, in contrast to SQUID arrays with identical junctions or with spreads in the critical currents.

Silicon-Based 3D Microfluidics for Parallelization of Droplet Generation.

Both the diversity and complexity of microfluidic systems have experienced a tremendous progress over the last decades, enabled by new materials, novel device concepts and innovative fabrication routes. In particular the subfield of high-throughput screening, used for biochemical, genetic and pharmacological samples, has extensively emerged from developments in droplet microfluidics. More recently, new 3D device architectures enabled either by stacking layers of PDMS or by direct 3D-printing have gained enormous attention for applications in chemical synthesis or biomedical assays. While the first microfluidic devices were based on silicon and glass structures, those materials have not yet been significantly expanded towards 3D despite their high chemical compatibility, mechanical strength or mass-production potential. In our work, we present a generic fabrication route based on the implementation of vertical vias and a redistribution layer to create glass-silicon-glass 3D microfluidic structures. It is used to build different droplet-generating devices with several flow-focusing junctions in parallel, all fed from a single source. We study the effect of having several of these junctions in parallel by varying the flow conditions of both the continuous and the dispersed phases. We demonstrate that the generic concept enables an upscaling in the production rate by increasing the number of droplet generators per device without sacrificing the monodispersity of the droplets.

Determination of the junction intrinsic recombination velocity of minority carriers in the base of parallel vertical multi junctions’ silicon solar cell using the open-circuit voltage calibration curve technique

Determination of the junction intrinsic recombination velocity of minority carriers in the base of parallel vertical multi junctions’ silicon solar cell using the open-circuit voltage calibration curve technique

The Rule of Thirds: Controlling Junction Chirality and Polarity in 3D DNA Tiles.

The successful self-assembly of tensegrity triangle DNA crystals heralded the ability to programmably construct macroscopic crystalline nanomaterials from rationally-designed, nanoscale components. This 3D DNA tile owes its "tensegrity" nature to its three rotationally stacked double helices locked together by the tensile winding of a center strand segmented into 7 base pair (bp) inter-junction regions, corresponding to two-thirds of a helical turn of DNA. All reported tensegrity triangles to date have employed turn inter-junction segments, yielding right-handed, antiparallel, "J1" junctions. Here a minimal DNA triangle motif consisting of 3-bp inter-junction segments, or one-third of a helical turn is reported. It is found that the minimal motif exhibits a reversed morphology with a left-handed tertiary structure mediated by a locally-parallel Holliday junction-the "L1" junction. This parallel junction yields a predicted helical groove matching pattern that breaks the pseudosymmetry between tile faces, and the junction morphology further suggests a folding mechanism. A Rule of Thirds by which supramolecular chirality can be programmed through inter-junction DNA segment length is identified. These results underscore the role that global topological forces play in determining local DNA architecture and ultimately point to an under-explored class of self-assembling, chiral nanomaterials for topological processes in biological systems.

Oligomeric CHMP7 mediates three-way ER junctions and ER-mitochondria interactions.

In metazoans the endoplasmic reticulum (ER) undergoes extensive remodeling during the cell cycle. The endosomal sorting complexes required for transport (ESCRT) protein CHMP7 coordinates ESCRT-III dependent nuclear envelope reformation during mitotic exit. However, potential roles of ER-associated CHMP7 at non-mitotic stages remain unclear. Here we discovered a new role of CHMP7 in mediating three-way ER and ER-mitochondrial membrane contact sites (MCSs). We showed that CHMP7 localizes to multiple cellular membranes including the ER, mitochondrial-associated membranes (MAMs) and the outer mitochondrial membrane (OMM) via its N-terminal membrane-binding domain. CHMP7 undergoes dynamic assembly at three-way ER junctions and ER-mitochondrial MCSs through hydrophobic interactions among α helix-1 and α helix-2 of the C-terminal CHMP-like domain, which was required for tethering different organelles in vivo. Furthermore, CHMP7 mediates the formation of three-way ER junctions in parallel with Atlastins (ATLs). Importantly, CHMP7 also regulates ER-mitochondrial interactions and its depletion affects mitochondrial division independently of ESCRT complex. Taken together, our results suggest a direct role of CHMP7 in the formation of the ER contacts in interphase.

A Novel Measurement Technique for Parallel-Connected Lithium-Ion Cells with Controllable Interconnection Resistance

Due to the broad use of parallel-connected cells across a wide variety of applications, it is essential to understand the current distribution between them. Variations in resistance, temperature and capacity can lead to an inhomogeneous current distribution and have a deleterious influence on ageing and safety. It is therefore crucial to investigate the current distribution within such systems. Many researchers have designed distinct test-benches to measure the current distribution. In any test-bench, known and unknown resistances caused by wiring, interconnections and measurement equipment can adversely affect the current distribution. The aim of this work is to design a low-complexity test apparatus that does not itself affect the current measurement.This work describes a novel measurement technique [1] to analyse the current distribution within parallel-connected cells without the use of complex custom-made test benches. While the cells are physically connected in conventional test benches, the proposed technique utilizes the software of a commercially available battery cycler to connect the cells in parallel. Because the software replaces the parallel junction within equations, this approach is called “virtual parallel connection“. Each cell is individually connected to the battery cycler and each cell voltage or current can be controlled separately. While a current pulse is used to determine the voltage across the reference cell, the control unit imposes the same voltage across each cell. Therefore, each cell benefits from the 4-wire measurement of the battery cycler, which generates no additional interconnection resistances. For this reason, only the Open Circuit Voltage (OCV), the capacity and the resistance of the cell itself, as well as its relationship to other cells can influence the current distribution. Additionally, any desired connection resistance can be chosen by adding a voltage drop in the equation of the battery cycler. Connecting cells virtually has many advantages, such as the ability to decouple the cells for check-ups and recouple them for cycling without ever touching them physically, independent location of each cell, scaling to n-parallel constellations, low assembly effort on the test-bench and defined contact resistances. In addition, different cell formats can be investigated with no additional effort.In this work, the virtual parallel connection will first be demonstrated, validated and discussed for constant current-, constant voltage- and rest phases using of a conventional test bench [2] within two NMC cells. Next, to understand the influence of additional resistances in two parallel-connected cells, two measurement studies were carried out in which interconnection resistances were varied between 0 and 5 mΩ. The first study investigates the influence of an inhomogeneous resistance increase within one of the parallel paths. Subsequently, the second study examines a homogeneous resistance increase within both parallel-connected paths.The conclusion of both studies is that the height of the local minima and maxima of the current distribution are mainly dependent on the resistance ratio of the parallel legs. The minima and maxima divide relative to the ratio of the combined cell and interconnection resistance in each pathway. In contrast, neither the local minima and maxima measured at various cumulative charge throughputs, nor the intersection points of the current distribution are affected by varied resistances. Meanwhile, OCV interactions between both cells determine the shape of the current distribution.Additionally, the shape of the Differential Voltage Analysis (DVA) showed correlations with current distribution. Some local minima and maxima within the current appear in almost the same region as the local minima and maxima of the DVA. By assigning different peaks of both half-cell profiles of the DVA to the anode and the cathode, the current distribution of both currents is expected to be affected by these characteristic peaks.

The Role of Coupling Radius in 1-D Parallel and 2-D SQUID and SQIF Arrays

We investigate theoretically the effect of the coupling radius on the transfer function in 1D parallel and 2D SQUID arrays with different number of Josephson junctions in parallel and series at 77 K. Our results show a plateauing of the array maximum transfer function with the number of junctions in parallel. The plateauing defines the array coupling radius which we show increases with decreasing the normalised inductive reactance of the SQUID loop. The coupling radius is found to be independent of the number of junctions in series. Finally, we investigate the voltage versus magnetic field response and maximum transfer function of one 1D and two 2D SQIF arrays with different SQUID loop area distributions.

Important Heat Contribution by Tunneling Spin Scattering in Magnetic Tunnel Junction

We investigated the heat contribution by tunneling spin scattering of magnetic tunnel junction in parallel (P) and antiparallel (AP) states using finite element simulation. It showed a maximum temperature increase of 23.2% from P to AP, which is even more significant than the heating asymmetry caused by different current directions. A remarkable enhancement of the temperature gradient was confirmed for contributing to the extra thermal spin-transfer torque to the free layer under a specific current direction. Both the contributions of enhanced temperature and temperature gradient should be the possible reasons for the asymmetry of the critical switching current density from P to AP and AP to P. We also extended the research to a double-barrier structure, clarifying its high performance from the aspect of heat generation. Our demonstration may offer efficient tunneling magnon excitation by using the tunneling spin scattering heat.

Josephson junctions in double nanowires bridged by in-situ deposited superconductors

We characterize parallel double quantum dot Josephson junctions based on closely-grown double nanowires bridged by in-situ deposited superconductors. The parallel double dot behavior occurs despite the closeness of the nanowires and the potential risk of nanowire clamping during growth. By tuning the charge filling and lead couplings, we map out the simplest parallel double quantum dot Yu-Shiba-Rusinov phase diagram. Our quasi-independent two-wire hybrids show promise for the realization of exotic topological phases.

High throughput production of microcapsules using microfluidics for self-healing of cementitious materials.

Capsule-based self-healing of cementitious materials is an effective way of healing cracks, significantly extending the life of structures, without imposing changes due to the incorporation of capsules into products during mixing. The methodologies currently being used for the development of capsules with a liquid core as a healing agent yield a wide range of sizes and shell thicknesses for the microcapsules, preventing a detailed assessment and optimisation of the microcapsule size and its effects. Uniquely, microfluidic technology offers precise control over the size and shell thickness through the formation of double emulsions. The drawback is that only small quantities of material can be typically produced. Here, by using paralleled junctions in a microfluidic device, high throughput production of materials was achieved, focusing for the first time on self-healing of cementitious materials. A microfluidic chip was assembled with 4 channels in parallel and selected hydrophobicity for the formation of the double emulsions. A coefficient of variation below 2.5% was observed for the 4 junctions, demonstrating the formation of monodisperse capsules. The control over the size and shell thickness by adjusting the flow rates was demonstrated, yielding capsules with an outer diameter of 615-630 μm and a shell thickness varying between 50 and 127 μm. By using triethanolamine as a surfactant, capsules with an aqueous core were produced. Furthermore, by selecting PEA, an acrylate with low tensile strength, the capsules embedded in the cement paste were successfully triggered to release the healing agent by crack formation. Capsules were successfully produced continuously for 7 h, with inner and outer diameters of 500 ± 31 μm and 656 ± 9 μm at a production rate of ∼13 g h-1 and a yield of around 80%. With these results and considering up to 6 chips in parallel, the production rate could be up to 1.5 kg per day. This demonstrates the huge potential of the microfluidic device with unique features to produce sufficiently large quantities of microcapsules for laboratory-scale assessment of self-healing performance.

Compact SQUID Realized in a Double-Layer Graphene Heterostructure.

2D systems that host 1D helical states are advantageous from the perspective of scalable topological quantum computation when coupled to a superconductor. Graphene is particularly promising for its high electronic quality, its versatility in van der Waals heterostructures, and its electron- and hole-like degenerate 0th Landau level. Here we study a compact double-layer graphene SQUID (superconducting quantum interference device), where the superconducting loop is reduced to the superconducting contacts connecting two parallel graphene Josephson junctions. Despite the small size of the SQUID, it is fully tunable by the independent gate control of the chemical potentials in both layers. Furthermore, both Josephson junctions show a skewed current-phase relationship, indicating the presence of superconducting modes with high transparency. In the quantum Hall regime, we measure a well-defined conductance plateau of 2e2/h indicative of counter-propagating edge channels in the two layers.