Josephson Weak Links Research Articles

Josephson weak link based on proximity effect in long bi-metallic thin-film bridge

Josephson weak link based on proximity effect in long bi-metallic thin-film bridge

Local internal demagnetizing fields as one of the main fundamental reasons for the low density of critical current in twinned YBa2Cu3O7 − x HTSCs

An oscillatory differential method of local approximation is applied to study the effect of local internal and external demagnetizing fields on the density of the critical current J c of intertwin Josephson weak links in YBCO HTSC samples. Demagnetizing fields H D1 and H D2 of samples with different J c and twin size d are measured in the zero field cooling and zero field cooling with magnetic flux accumulation modes. The following parameters are determined: the twin size d, the thermodynamic first critical magnetic fields of twins Hi c1, the demagnetizing fields of twins H Dtr, the densities of intertwin effective critical currents J ceff, the critical pinning currents J cp, and the Meissner screening critical currents J cg. It is shown that, at the fields Hi c1, large twins are stepwise decomposed into a group of smaller twins with close demagnetizing factors. It is found that an increase in J cg and J ceff and a decrease in d lead, on the one hand, to a decrease in J c due to an increase in H D and H Dtr produced by J ceff and J cg, and, on the other hand, to an increase in J ceff and J cg due to a decrease in d. For samples with large J c and d, as well as for samples with low values of J c and d in a field of about 8 × 10−2 T, H D and H Dtr suppress J c by about 70% and 60%, respectively. According to the results obtained in the present study and the known literature data, J c decreases with increasing J cg; in this case, a decrease in d leads to a decrease, rather than an increase, in J c. Since the weak links and low values of J c are fundamental properties of HTSCs, the literature data should be corrected with regard to the important facts on the effect of H D and H Dtr on J c.

Gate-Defined Josephson weak-Links in Monolayer WTe2.

Systems combining superconductors with topological insulators offer a platform for the study of Majorana bound states and a possible route to realize fault tolerant topological quantum computation. Among the systems being considered in this field, monolayers of tungsten ditelluride (WTe2 ) have a rare combination of properties. Notably, it has been demonstrated to be a Quantum Spin Hall Insulator (QSHI) and can easily be gated into a superconducting state. Wereport measurements on gate-defined Josephson weak-link devices fabricated using monolayer WTe2 . It is found that consideration of the two dimensional superconducting leads are critical in the interpretation of magnetic interference in the resulting junctions. The reported fabrication procedures suggest a facile way to produce further devices from this technically challenging material and the results mark the first step toward realizing versatile all-in-one topological Josephson weak-links using monolayer WTe2 . This article is protected by copyright. All rights reserved.

Внешние и внутренние поля размагничивания как одна из основных фундаментальных причин низкой плотности критического тока двойниковых высокотемпературных сверхпроводников YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-x-=/SUB=-

An oscillatory differential method of local approximation is applied to study the effect of local internal and external demagnetizing fields on the density of the critical current Jc of intertwin Josephson weak links in YBCO HTSC samples. Demagnetizing fields HD1 and HD2 of samples with different Jc and twin size d are measured in the ZFC and ZFCMFA modes. The following parameters are determined: the twin size d, the thermodynamic first critical magnetic fields of twins Hic1, the demagnetizing fields of twins HDtr, the densities of intertwin effective critical currents Jceff, the critical pinning currents Jcp, and the Meissner screening critical currents Jcg. It is shown that, at the fields Hic1, large twins are stepwise decomposed into a group of smaller twins with close demagnetizing factors. It is found that an increase in Jcg and Jceff and a decrease in d lead, on the one hand, to a decrease in Jc due to an increase in HD and HDtr produced by Jceff and Jcg, on the other hand, to an increase in Jceff and Jcg due to a decrease in d. For samples with large Jc and d, as well as for samples with low values of Jc and d in a field of about 810-2 T, HD and HDtr suppress Jc by about 70% and 60%, respectively. According to the results obtained in the present study and the known literature data, Jc decreases with increasing Jcg; in this case, a decrease in d leads to a decrease, rather than an increase, in Jc. Since the weak links and low values of Jc are fundamental properties of HTSCs, the literature data should be corrected with regard to the important facts on the effect of HD and HDtr on Jc.

Inductive Superconducting Quantum Interference Proximity Transistor: The L-SQUIPT

The design for an inductive superconducting quantum interference proximity transistor with enhanced performance, the L-SQUIPT, is presented and analyzed. The interferometer is based on a double-loop structure, where each ring comprises a superconductor-normal metal-superconductor mesoscopic Josephson weak-link and the read-out electrode is implemented in the form of a superconducting tunnel probe. Our design allows both to improve the coupling of the transistor to the external magnetic field and to increase the characteristic magnetic flux transfer functions, thereby leading to an improved ultrasensitive quantum limited magnetometer. The L-SQUIPT behavior is analyzed in both the dissipative and the dissipationless Josephson-like operation modes, in the dissipative or in the dissipationless Josephson-like operation mode in the latter case by exploiting both an inductive and a dispersive readout scheme. The improved performance makes the L-SQUIPT promising for magnetic field detection as well as for specific applications in quantum technology, where a responsive dispersive magnetometry at milliKelvin temperatures is required.

Cooper pairs localization in tree-like networks of superconducting islands

We study inhomogeneous Cooper pairs distribution and localization effects in tree-like networks of superconducting islands coupled via Josephson weak links. Using a generalized Feynman’s approach, reminiscent of the Bose–Hubbard model, we demonstrate that the Cooper pairs fraction which localizes on a specific network’s island is limited by the network topology and, if present, by the repulsive interaction. These findings contribute to clarify the interplay between confinement effects induced by the network’s topology and interaction and shed some light on recent experiments dealing with networks of Josephson junctions.

Superconducting Bio-Inspired Au-Nanowire-Based Neurons.

High-performance modeling of neurophysiological processes is an urgent task that requires new approaches to information processing. In this context, two- and three-junction superconducting quantum interferometers with Josephson weak links based on gold nanowires are fabricated and investigated experimentally. The studied cells are proposed for the implementation of bio-inspired neurons—high-performance, energy-efficient, and compact elements of neuromorphic processor. The operation modes of an advanced artificial neuron capable of generating the burst firing activation patterns are explored theoretically. A comparison with the Izhikevich mathematical model of biological neurons is carried out.

Signatures of Interactions in the Andreev Spectrum of Nanowire Josephson Junctions.

We performed microwave spectroscopy of an InAs nanowire between superconducting contacts implementing a finite-length, multichannel Josephson weak link. Certain features in the spectra, such as the splitting by spin-orbit interactions of the transition lines among Andreev states, have been already understood in terms of noninteracting models. However, we identify here additional transitions, which evidence the presence of Coulomb interactions. By combining experimental measurements and model calculations, we reach a qualitative understanding of these very rich Andreev spectra.

Supercurrent parity meter in a nanowire Cooper pair transistor.

We study a Cooper pair transistor realized by two Josephson weak links that enclose a superconducting island in an InSb-Al hybrid nanowire. When the nanowire is subject to a magnetic field, isolated subgap levels arise in the superconducting island and, because of the Coulomb blockade, mediate a supercurrent by coherent cotunneling of Cooper pairs. We show that the supercurrent resulting from such cotunneling events exhibits, for low to moderate magnetic fields, a phase offset that discriminates even and odd charge ground states on the superconducting island. Notably, this phase offset persists when a subgap state approaches zero energy and, based on theoretical considerations, permits parity measurements of subgap states by supercurrent interferometry. Such supercurrent parity measurements could, in a series of experiments, provide an alternative approach for manipulating and protecting quantum information stored in the isolated subgap levels of superconducting islands.

Spin coherent manipulation in Josephson weak links

Novel designs of Josephson weak links based on semiconducting nanowires combined with circuit QED techniques have enabled the resolution of their fine structure due to spin-orbit interactions, opening a path towards Andreev spin qubits. Nevertheless, direct manipulation of the spin within a given Andreev state is in general suppressed compared to inter-doublet manipulation in the absence of Zeeman effects. In addition, noisy spin-flip mechanisms limit any coherent manipulation protocol to spin post-selection. We propose a combination of a spin polarization protocol analogous to sideband cooling with stimulated Raman adiabatic passage specifically tailored for these systems. We show this approach is robust for a large range of design parameters, including the currently rather stringent coherence times.

Stochastic Resonance in Thermally Bistable Josephson Weak Links and Micro-SQUIDs

Constriction-based Josephson weak-links display a thermal bi-stability between two states exhibiting zero and finite voltages. This manifests in experiments either as hysteresis in weak-links current voltage characteristics or as random telegraphic signal in voltage. In the latter case, a noise-driven amplification of a sinusoidal excitation of the device is observed, at frequencies matching the characteristic switching frequency in telegraphic signal, a phenomenon known as stochastic resonance. The observed behavior is understood using a two-state model of stochastic resonance and is exploited to illustrate an enhanced signal-to-noise-ratio in a micro-SQUID as a magnetic field sensor.

Circuit-QED with phase-biased Josephson weak links

By coupling a superconducting weak link to a microwave resonator, recent experiments probed the spectrum and achieved the quantum manipulation of Andreev states in various systems. However, the quantitative understanding of the response of the resonator to changes in the occupancy of the Andreev levels, which are of fermionic nature, is missing. Here, using Bogoliubov-de Gennes formalism to describe the weak link and a general formulation of the coupling to the resonator, we calculate the shift of the resonator frequency as a function of the levels occupancy and describe how transitions are induced by phase or electric field microwave drives. We apply this formalism to analyze recent experimental results obtained using circuit-QED techniques on superconducting atomic contacts and semiconducting nanowire Josephson junctions.

Circuit-QED with phase-biased Josephson weak links

Circuit-QED with phase-biased Josephson weak links

Vanadium gate-controlled Josephson half-wave nanorectifier

Recently, the possibility to tune the critical current of conventional metallic superconductors via electrostatic gating was shown in wires, Josephson weak-links, and superconductor-normal metal–superconductor junctions. Here, we exploit such a technique to demonstrate a gate-controlled vanadium-based Dayem nano-bridge operated as a half-wave rectifier at 3 K. Our devices exploit the gate-driven modulation of the critical current of the Josephson junction and the resulting steep variation of its normal-state resistance, to convert an AC signal applied to the gate electrode into a DC one across the junction. All-metallic superconducting gated rectifiers could provide the enabling technology to realize tunable photon detectors and diodes useful for superconducting electronics circuitry.

Electrostatic Control of Phase Slips in Ti Josephson Nanotransistors

The investigation of the switching current probability distribution of a Josephson junction is a conventional tool to gain information on the phase slips dynamics as a function of the temperature. Here we adopt this well-established technique to probe the impact of an external static electric field on the occurrence of phase slips in gated all-metallic titanium (Ti) Josephson weak links. We show, in a temperature range between 20 mK and 420 mK, that the evolution of the phase slips dynamics as a function of the electrostatic field starkly differs from that observed as a function of the temperature. This fact demonstrates, on the one hand, that the electric field suppression of the critical current is not simply related to a conventional thermal-like quasiparticle overheating in the weak-link region. On the other hand, our results may open the way to operate an electrostatic-driven manipulation of phase slips in metallic Josephson nanojunctions, which can be pivotal for the control of decoherence in superconducting nanostructures.

The discovery, disappearance and re-emergence of radiation-stimulated superconductivity

We trace the historical fate of experiment and theory of microwave-stimulated superconductivity as originally reported for constriction-type superconducting weak links. It is shown that the observed effect disappeared by improving weak links to obtain the desired Josephson properties. Separate experiments were carried out to evaluate the validity of the proposed theory of Eliash’berg for energy-gap-enhancement in superconducting films in a microwave field, without reaching a full quantitatively reliable measurement of the stimulated energy gap in a microwave field, but convincing enough to understand the earlier deviations from the Josephson-effect. Over the same time period microwave-stimulated superconductivity continued to be present in superconductor-normal metal-superconductor Josephson weak links. This experimental body of work was left unexplained for several decades and could only be understood properly after the microscopic theory of the proximity-effect had matured enough, including its non-equilibrium aspects. It implies that the increase in critical current in weak-link Josephson-junctions is due to an enhancement of the phase-coherence rather than to an enhancement of the energy-gap as proposed by Eliash’berg. The complex interplay between proximity-effect and the occupation of states continues to be, in a variety of ways, at the core of the ongoing research on hybrid Josephson-junctions. The subject of radiation-enhanced superconductivity has re-emerged in the study of the power-dependence of superconducting microwave resonators, but also in the light-induced emergence of superconductivity in complex materials.

Quasiclassical theory for interfaces with spin-orbit coupling

In recent years, substantial progress has been made regarding the application of quasiclassical theory on superconducting hybrid structures. This theoretical framework is reliant on a proper set of boundary conditions in order to describe multilayered systems. With the advent of the field of superconducting spintronics, systems which combine heavy metal layers, in which there is large spin--orbit coupling, with ferromagnets have received a great deal of attention, due to their potential for generating long range triplet superconductivity. In contrast to interfaces of strongly spin polarized materials, which are well understood, a quasiclassical theory for interfaces in systems where there is significant spin--orbit coupling does not yet exist. After reviewing the quasiclassical theory for interfaces, we here solve this problem by deriving a new set of boundary conditions which take spin--orbit coupling explicitly into account. We then go on to apply these boundary conditions to a superconductor-ferromagnet (SF) bilayer and an SFS Josephson weak link, demonstrating the emergence of long range triplet superconductivity in these systems.

Broadband microwave spectroscopy of semiconductor nanowire-based Cooper-pair transistors

The Cooper-pair transistor (CPT), a small superconducting island enclosed between two Josephson weak links, is the atomic building block of various superconducting quantum circuits. Utilizing gate-tunable semiconductor channels as weak links, the energy scale associated with the Josephson tunneling can be changed with respect to the charging energy of the island, tuning the extent of its charge fluctuations. Here, we directly demonstrate this control by mapping the energy level structure of a CPT made of an indium arsenide nanowire (NW) with a superconducting aluminum shell. We extract the device parameters based on the exhaustive modeling of the quantum dynamics of the phase-biased nanowire CPT and directly measure the even-odd parity occupation ratio as a function of the device temperature, relevant for superconducting and prospective topological qubits.

Inter-granular effects at high magnetic fields of cuprate and iron chalcogenide superconducting materials

The weak links effects are one of the main challenges for effective power applications of high temperature superconducting materials. Studies of these effects help for their better understanding and subsequent improvement. An overview analysis of the intergranular properties of cuprate (Y0.8Ca0.2Ba2Cu3O7-δ) and iron-based chalcogenide (FeSe0.5Te0.5) polycrystalline samples was carried out, by means of series of electro-transport experiments at different magnetic fields. The temperature evolution of the Josephson coupling and intrinsic superconductivity effects for the both systems was constructed. The FeSe0.5Te0.5 compound shows very stable and superior behavior compared to Y0.8Ca0.2BCO up to the highest magnetic fields (14T) used. We have explored FeSe0.5Te0.5 Josephson weak links influence (as a non-linear process) over the resistive transition using different AC current amplitudes and applying the sensitive AC transport third harmonics technique.

Pico pulse response analysis of Josephson weak-link using time-dependent Ginzburg-Landau model

The pulse wave whose width is picosecond is called the pico pulse. In this paper, the pico pulse response analysis of high Tc superconducting Josephson weak-link made of Bi2Sr2Ca2Cu3O10 in the Terahertz (THz) region is reported. Since the photon energy of the THz radiation is greater than the energy gap of high Tc superconductor, the one dimensional time-dependent Ginzburg–Landau (TDGL) equation is used and the TDGL model as the equivalent circuit of Josephson weak-link instead of the Resistively-Shunted-Junction model is derived by use of the TDGL equation. It is found that the peak value of pulse response decreases when the pulse width decreases.