Junction Arrays Research Articles

Theory for Dissipative Time Crystals in Coupled Parametric Oscillators.

Discrete time crystals are novel phases of matter that break the discrete time translational symmetry of a periodically driven system. In this Letter, we propose a classical system of weakly nonlinear parametrically driven coupled oscillators as a test bed to understand these phases. Such a system of parametric oscillators can be used to model period-doubling instabilities of Josephson junction arrays as well as semiconductor lasers. To show that this instability leads to a discrete time crystal we first show that a certain limit of the system is close to Langevin dynamics in a symmetry breaking potential. We numerically show that this phase exists even in the presence of Ising symmetry breaking using a Glauber dynamics approximation. We then use a field theoretic argument to show that these results are robust to other approximations including the semiclassical limit when applied to dissipative quantum systems.

Bose Metals, from Prediction to Realization.

Bose metals are metals made of Cooper pairs, which form at very low temperatures in superconducting films and Josephson junction arrays as an intermediate phase between superconductivity and superinsulation. We predicted the existence of this 2D metallic phase of bosons in the mid 1990s, showing that they arise due to topological quantum effects. The observation of Bose metals in perfectly regular Josephson junction arrays fully confirms our prediction and rules out alternative models based on disorder. Here, we review the basic mechanism leading to Bose metals. The key points are that the relevant vortices in granular superconductors are core-less, mobile XY vortices which can tunnel through the system due to quantum phase slips, that there is no charge-phase commutation relation preventing such vortices from being simultaneously out of condensate with charges, and that out-of-condensate charges and vortices are subject to topological mutual statistics interactions, a quantum effect that dominates at low temperatures. These repulsive mutual statistics interactions are sufficient to increase the energy of the Cooper pairs and lift them out of condensate. The result is a topological ground state in which charge conduction along edges and vortex movement across them organize themselves so as to generate the observed metallic saturation at low temperatures. This state is known today as a bosonic topological insulator.

Superconductor to metal quantum phase transition with magnetic field in Josephson coupled lead islands on Graphene

Abstract Superconductor-to-metal transition with magnetic field and gate-voltage is studied in a Josephson junction array comprising of randomly distributed lead islands on exfoliated single-layer graphene. The superconductivity onset temperature at low magnetic-fields is fitted to the Werthamer-Helfand-Hohenberg theory to model the temperature dependence of the upper critical field. The magnetoresistance in the intermediate temperature and field regime is described using thermally activated flux flow dictated by field dependent activation barrier. The barrier also depends on the gate voltage which dictates the inter-island Josephson coupling and disorder. The magnetoresistance near the upper critical field at low temperatures shows signatures of a gate dependent continuous quantum phase transition between superconductor and metal. The finite size scaling analysis shows that this transition belongs to the $(2+1)$D-XY universality class without disorder.

Room-Temperature Superconductivity in 1D

We review the theoretical model underpinning the recently reported room-temperature, ambient-pressure superconductivity along line defects on the surface of highly oriented pyrolytic graphite. The main ingredients for this 1D room-temperature superconductivity are pairing by effective strain gauge fields, the formation of an effective Josephson junction array in its Bose metal state on the surface and the suppression of phase slips by dimensional embedding in an extremely well-conducting 3D bulk structure.

A Voltage Monitoring Approach for Faster Reducing Flux Trapping in Josephson Junction Arrays

A Voltage Monitoring Approach for Faster Reducing Flux Trapping in Josephson Junction Arrays

On mathematical analysis of synchronization of bidirectionally coupled Kuramoto oscillators under inertia effect

In this article, we analyze the phase synchronization and frequency synchronization for the bidirectionally coupled Kuramoto model under the effect of inertia. Unlike the classical Kuramoto model equipped with all-to-all coupled interaction, in the setting of this model, each oscillator θi only interacts directly with θi+1 and θi−1. The bidirectional interaction is a typical setting of the concatenation in power systems. Additionally, it is necessary to impose the effect of inertia in the Kuramoto model in the applications such as power systems and Josephson junction array. In this article, we first present a theory of the global convergence for frequency synchronization for the identical case. For the non-identical case, we prove that the second-order bidirectionally coupled Kuramoto model exhibits a frequency synchronization if the coupling strength is large, inertia is small, and all oscillators are initially confined to a sector. We emphasize that the arc length of this sector possesses a positive lower bound which is independent of the number of oscillators. If, in addition, all natural frequencies are identical, we further show that the phase synchronization emerges. Moreover, we demonstrate the numerical simulations to support the main results. On the other hand, we observe that the model equipped with large inertia can exhibit the synchronization. Exploring the synchronization theory for large inertia case is left as the future work.

Electrically Driven Deterministic Plasmon Light Sources Based on Arrays of Molecular Tunnel Junctions.

Surface plasmons excited via inelastic tunnelling have led to plasmon light sources with small footprints and ultrafast response speeds, which are favored by integrated optical circuits. Self-assembled monolayers of organic molecules function as highly tunable tunnel barriers with novel functions. However, limited by the low effective contact between the liquid metal electrode and the self-assembled monolayers, it is quite challenging to obtain molecular plasmon light sources with high density and uniform emission. Here, by combining lithographic patterning with a solvent treatment method, we have demonstrated electrically driven deterministic plasmon emission from arrays of molecular tunnel junctions. The solvent treatment could largely improve the effective contact from 9.6% to 48% and simultaneously allow the liquid metal to fill into lithographically patterned micropore structures toward deterministic plasmon emission with desired patterns. Our findings open up new possibilities for tunnel junction-based plasmon light sources, laying the foundation for electrically driven light-emitting metasurfaces.

Electromigrated Gold Nanogap Tunnel Junction Arrays: Fabrication and Electrical Behavior in Liquid and Gaseous Media.

Tunnel junctions have been suggested as high-throughput electronic single molecule sensors in liquids with several seminal experiments conducted using break junctions with reconfigurable gaps. For practical single molecule sensing applications, arrays of on-chip integrated fixed-gap tunnel junctions that can be built into compact systems are preferable. Fabricating nanogaps by electromigration is one of the most promising approaches to realize on-chip integrated tunnel junction sensors. However, the electrical behavior of fixed-gap tunnel junctions immersed in liquid media has not been systematically studied to date, and the formation of electromigrated nanogap tunnel junctions in liquid media has not yet been demonstrated. In this work, we perform a comparative study of the formation and electrical behavior of arrays of gold nanogap tunnel junctions made by feedback-controlled electromigration immersed in various liquid and gaseous media (deionized water, mesitylene, ethanol, nitrogen, and air). We demonstrate that tunnel junctions can be obtained from microfabricated gold nanoconstrictions inside liquid media. Electromigration of junctions in air produces the highest yield (61-67%), electromigration in deionized water and mesitylene results in a lower yield than in air (44-48%), whereas electromigration in ethanol fails to produce viable tunnel junctions due to interfering electrochemical processes. We map out the stability of the conductance characteristics of the resulting tunnel junctions and identify medium-specific operational conditions that have an impact on the yield of forming stable junctions. Furthermore, we highlight the unique challenges associated with working with arrays of large numbers of tunnel junctions in batches. Our findings will inform future efforts to build single molecule sensors using on-chip integrated tunnel junctions.

High-bandwidth low-current measurement system for automated and scalable probing of tunnel junctions in liquids.

Tunnel junctions have long been used to immobilize and study the electronic transport properties of single molecules. The sensitivity of tunneling currents to entities in the tunneling gap has generated interest in developing electronic biosensors with single molecule resolution. Tunnel junctions can, for example, be used for sensing bound or unbound DNA, RNA, amino acids, and proteins in liquids. However, manufacturing technologies for on-chip integrated arrays of tunnel junction sensors are still in their infancy, and scalable measurement strategies that allow the measurement of large numbers of tunneling junctions are required to facilitate progress. Here, we describe an experimental setup to perform scalable, high-bandwidth (>10kHz) measurements of low currents (pA-nA) in arrays of on-chip integrated tunnel junctions immersed in various liquid media. Leveraging a commercially available compact 100kHz bandwidth low-current measurement instrument, we developed a custom two-terminal probe on which the amplifier is directly mounted to decrease parasitic probe capacitances to sub-pF levels. We also integrated a motorized three-axis stage, which could be powered down using software control, inside the Faraday cage of the setup. This enabled automated data acquisition on arrays of tunnel junctions without worsening the noise floor despite being inside the Faraday cage. A deliberately positioned air gap in the fluidic path ensured liquid perfusion to the chip from outside the Faraday cage without coupling in additional noise. We demonstrate the performance of our setup using rapid current switching observed in electromigrated gold tunnel junctions immersed in deionized water.

Quantum Simulation of the Tricritical Ising Model in Tunable Josephson Junction Ladders.

Modern hybrid superconductor-semiconductor Josephson junction arrays are a promising platform for analog quantum simulations. Their controllable and nonsinusoidal energy-phase relation opens the path to implement nontrivial interactions and study the emergence of exotic quantum phase transitions. Here, we propose the analysis of an array of hybrid Josephson junctions defining a two-leg ladder geometry for the quantum simulation of the tricritical Ising phase transition. This transition provides the paradigmatic example of minimal conformal models beyond Ising criticality and its excitations are intimately related to Fibonacci non-Abelian anyons and topological order in two dimensions. We study this superconducting system and its thermodynamic phases based on bosonization and matrix-product-state techniques. Its effective continuous description in terms of a three-frequency sine-Gordon quantum field theory suggests the presence of the targeted tricritical point and the numerical simulations confirm this picture. Our results indicate which experimental observables can be adopted in realistic devices to probe the physics and the phase transitions of the model. Additionally, our proposal provides a useful one-dimensional building block to design exotic topological order in two-dimensional scalable Josephson junction arrays.

MgB[formula omitted] Josephson Junctions fabricated by Focused Helium Ion Beam with different irradiation doses on SiC and MgO substrates

Recently, high quality MgB2 single junctions and junction arrays fabricated by Focused Helium Ion Beam irradiation (He-FIB) have been reported. However, the effects of irradiation doses and substrates on junction properties have not been analysed systematically. In this work, 30 nm MgB2 thin films were deposited on SiC (0001) and MgO (111) substrates using Hybrid Physical–Chemical Vapour Deposition (HPCVD) technique and then etched into 2–4 μm wide microbridges. 2000–6000 ions/nm doses of He-FIB were irradiated across these microbridges, creating narrow junction barriers. R–T curves exhibit a clear foot-like structure that enlarges as irradiation dose increases. Temperature dependence of junction properties (critical current Ic, junction normal state resistance Rn, characteristic voltage Vc) shows that all junctions in our experiment exhibit superconductor–normal–superconductor (SNS) like behaviour and higher irradiation doses create thicker junction barriers. Furthermore, we analyse junction properties dependence on irradiation doses which yields an exponential change law. Finally, Fraunhofer diffraction-like patterns and Shapiro steps of junctions are also measured. Our results show MgB2 Josephson Junctions with adjustable properties can be fabricated by He-FIB on SiC and MgO substrates, which provides a solid foundation for future application devices research.

Heat Bath in a Quantum Circuit.

We discuss the concept and realization of a heat bath in solid state quantum systems. We demonstrate that, unlike a true resistor, a finite one-dimensional Josephson junction array or analogously a transmission line with non-vanishing frequency spacing, commonly considered as a reservoir of a quantum circuit, does not strictly qualify as a Caldeira-Leggett type dissipative environment. We then consider a set of quantum two-level systems as a bath, which can be realized as a collection of qubits. We show that only a dense and wide distribution of energies of the two-level systems can secure long Poincare recurrence times characteristic of a proper heat bath. An alternative for this bath is a collection of harmonic oscillators, for instance, in the form of superconducting resonators.

Measurement-driven neural-network training for integrated magnetic tunnel junction arrays

Measurement-driven neural-network training for integrated magnetic tunnel junction arrays

Braiding Operations for a Topological Josephson Junction Array Using a Bipolar Current Pulse Generator Controlled by SFQ Logic Circuits

Braiding Operations for a Topological Josephson Junction Array Using a Bipolar Current Pulse Generator Controlled by SFQ Logic Circuits

Josephson junction arrays as a platform for topological phases of matter

Josephson junction arrays as a platform for topological phases of matter

Thouless pumping in Josephson junction arrays

Recent advancements in fabrication techniques have enabled unprecedented clean interfaces and gate tunability in semiconductor-superconductor heterostructures. Inspired by these developments, we propose protocols to realize Thouless quantum pumping in electrically tunable Josephson junction arrays. We analyze, in particular, the implementation of the Rice-Mele and the Harper-Hofstadter pumping schemes, whose realization would validate these systems as flexible platforms for quantum simulations. We investigate numerically the long-time behavior of chains of controllable superconducting islands in the Coulomb-blockaded regime. Our findings provide new insights into the dynamics of periodically driven interacting systems and highlight the robustness of Thouless pumping with respect to boundary effects typical of superconducting circuits.

Large area arrays of discrete single-molecule junctions derived from host-guest complexes.

The desire to continually reduce the lower limits of semiconductor integrated circuit (IC) fabrication methods continues to inspire interest in unimolecular electronics as a platform technology for the realization of future (opto)electronic devices. However, despite successes in developing methods for the construction and measurement of single-molecule and large-area molecular junctions, exercising control over the precise junction geometry remains a significant challenge. Here, host-guest complexes of the wire-like viologen derivative 1,1'-bis(4-(methylthio)-phenyl)-[4,4'-bipyridine]-1,1'-diium chloride ([1][Cl]2) and cucurbit[7]uril (CB[7]) have been self-assembled in a regular pattern over a gold substrate. Subsequently, ligandless gold nanoparticles (AuNPs) synthesized in situ are deposited over the host-guest array. The agreement between the conductance of individual mono-molecular junctions, appropriately chosen as a function of the AuNP diameter, within this array determined by conductive probe atomic force microscope (c-AFM) and true single-molecule measurements for a closely similar host-guest complex within a scanning tunneling microscope break-junction (STM-BJ) indicates the formation of molecular junctions derived from these host-guest complexes without deleterious intermolecular coupling effects.

In situ construction of PtSe2/Ge Schottky junction array with interface passivation for broadband infrared photodetection and imaging

AbstractInfrared (IR) detection is vital for various military and civilian applications. Recent research has highlighted the potential of two‐dimensional (2D) topological semimetals in IR detection due to their distinctive advantages, including van der Waals (vdW) stacking, gapless electronic structure, and Van Hove singularities in the electronic density of states. However, challenges such as large‐scale patterning, poor photoresponsivity, and high dark current of photodetectors based on 2D topological semimetals significantly impede their wider applications in low‐energy photon sensing. Here, we demonstrate the in situ fabrication of PtSe2/Ge Schottky junction by directly depositing 2D PtSe2 films with a vertical layer structure on a Ge substrate with an ultrathin AlOx layer. Due to high quality junction, the photodetector features a broadband response of up to 4.6 μm, along with a high specific detectivity of ~1012 Jones, and operates with remarkable stability in ambient conditions as well. Moreover, the highly integrated device arrays based on PtSe2/AlOx/Ge Schottky junction showcases excellent Mid‐IR (MIR) imaging capability at room temperature. These findings highlight the promising prospects of 2D topological semimetals for uncooled IR photodetection and imaging applications.image

Topological Gauge Theory of Josephson Junction Arrays: The Discovery of Superinsulation

We review the topological gauge theory description of Josephson junction arrays (JJA), fabricated systems which exhibit the superconductor-to-insulator transition (SIT). This description revealed the topological nature of the phases around the SIT and led to the discovery of a new state of matter, the superinsulator, characterized by infinite resistance, even at finite temperatures, due to linear confinement of electric charges. This discovery is particularly relevant for the physics of superconducting films with emergent granularity, which are modeled with JJAs and share the same phase diagram.

Resistivity Tensor of Vortex-Lattice States in Josephson Junction Arrays.

Two-dimensional Josephson junction arrays frustrated by a perpendicular magnetic field are predicted to form a cascade of distinct vortex lattice states. Here, we show that the resistivity tensor provides both structural and dynamical information on the vortex-lattice states and intervening phase transitions, which allows for experimental identification of these symmetry-breaking ground states. We illustrate our general approach by a microscopic theory of the resistivity tensor for a range of magnetic fields exhibiting a rich set of vortex lattices as well as transitions to liquid-crystalline vortex states.