Superconducting Films Research Articles

A super-stretchable conductive film with strain-insensitive conductivity for stretchable EMI shielding materials and wearable capacitive strain sensors

Strain-insensitive conductive films as stretchable electromagnetic interference (EMI) shielding materials and stretchable electrodes are highly desired in wearable electronics. However, fabricating super strain-insensitive conductive films under a tensile strain higher than 400 % is still a great challenge. Herein, a super-stretchable conductive film based on the crumple-structured Ti3C2Tx nanosheets-single walled carbon nanotubes/stretchable substrate double-layers is designed for the stretchable EMI shielding materials and electrodes. The resulting film exhibits a strain-insensitive electrical conductivity as high as 3.01 × 103 S/m even at a strain up to 500 %, which endows the film with a high and stable electromagnetic interference shielding efficiency (EMI SE) value of ∼45 dB. More interestingly, the EMI SE value of the film remains nearly constant even after 2000 cycles of 500 % tensile strain, indicating the excellent long-term service stability as a stretchable EMI shielding material. Moreover, a capacitive strain sensor with extra-wide sensing range, ultra-high stability, and excellent durability is successfully achieved by employing the as-prepared films as stretchable electrodes. This work proposes a convenient strategy of strain-insensitive conductive film aiming to design stretchable EMI shielding materials and electrodes for wearable electronics.

Vortex confinement through an unquantized magnetic flux

Geometrically confined superconductors often experience a breakdown in the quantization of magnetic flux owing to the incomplete screening of the supercurrent against field penetration. In this study, we report that magnetic field confinement occurs regardless of the dimensionality of the system, even extending to 1D linear potential systems. By using a vector-field magnetic force microscope, we successfully create a vortex‒antivortex pair connected by a 1D unquantized magnetic flux in ultrathin superconducting films. Through an investigation of the manipulation and thermal behavior of the vortex pair, we uncover a long-range interaction mediated by the unquantized magnetic flux. These findings suggest a universal phenomenon of unquantized magnetic flux formation, independent of the geometry of the system. Our results present an experimental route for investigating the impact of confinement on superconducting properties and order parameters in unconventional superconductors characterized by extremely low dimensionality.

Single-coated thick superconducting films for metal–organic deposition using trifluoroacetates

Metal-organic deposition using trifluoroacetates (TFA-MOD) is known to yield uniform superconducting wires by a liquid growth mode. However, it has been difficult to prepare thick films because of drying stress during the calcining process. To avoid the drying stress, conventional crack-preventing chemicals such as H(CH2)8COOH are applied in conventional metal–organic deposition. However, large amounts of hydrogen atoms react with fluorine atoms during calcining process in TFA-MOD, and the consequent increased harmful carbon residue decreases superconductivity of the resulting films. To avoid the chemical reaction, new crack-preventing chemicals such as H(CF2)8COOH were applied to prepare single-coated thick films. A low ratio of hydrogen atoms decreases the chemical reaction and generates hydrogen fluorine gas, consequently suppressing the carbon residue. Above the calcining temperature, the crack-preventing chemical is decomposed into low-boiling-point chemicals such as CF2CF2 or CF3CF3. Consequently, single-coated thick film having low carbon residue and sufficient superconducting current per width was realized. For a long time, the authors have studied other possible candidate crack-preventing chemicals. Newly introduced fluorine ion measurement of decomposed materials during the calcining process revealed the nature of the crack-preventing chemicals. Based on the accumulated results, we have concluded that among over one million chemicals there are only two groups suitable for preparing single-coated thick superconducting films by TFA-MOD. One group is hydrogenated perfluoro-carboxylic acids such as H(CF2)8COOH and the other group is perfluoro di-carboxylic acids. With H(CF2)8COOH, using a single-coating process we were able to achieve a 560 nm-thick YBa2Cu3O6.93 film having Jc of 4.70 MA/cm2 (77 K,0T). Compared with a standard 150 nm-thick YBa2Cu3O6.93 film having Jc of 7.70 MA/cm2 (77 K,0T), the critical current per width is improved to about 227 %.

Two-phase/two-gap scenario in heavily reduced superconducting ITO films revealed by point-contact spectroscopy

We present the first point-contact measurements of heavily reduced indium tin oxide (ITO) films in the superconducting state, which simultaneously demonstrate high transparency in the visible light spectrum. Analysis of the differential conductance spectrum indicates the presence of two superconducting phases, the main one with a critical temperature Tc of about 4.6 K and an additional phase with Tc ∼ 10 K, most likely localized near the surface. The phase separation is indirectly confirmed by resistance measurements of the layers and ab initio calculations of the doped ITO electronic structure. The results obtained give hope for the creation of transparent superconducting films with critical temperatures of about 10 K.

Correlating critical current density, quench protection, relaxation time and entropy in superconductors after disturbances—Intermediate summary

<p>This paper summarizes results recently obtained from simulation of transient temperature excursions in filamentary and thin film superconductors. Under multi-component heat transfer in the complicated conductor cross sections and materials composition of present High Temperature Superconductors, numerical, Finite Element and Monte Carlo simulations are applied to solve Fourier’s differential equation with high spatial and temporal resolution. The overall aim was to encircle the quench problem in superconductors and to provide new stability criteria from correlations between superconductor critical current density, density of electron pairs, and relaxation time and entropy. Relaxation, correlation and entropy analysis presented in this paper extends the spectrum of standard methods to avoid quench to a new tool. As results, quench starts always locally, and as a highlight of this investigation, a second “critical” temperature, <em>T<sub>Quench</sub></em>, has been identified that with high probability exists below standard critical temperature. Entropy is the driving force for relaxation of the superconductor to new equilibrium after a disturbance.<strong></strong></p>

Assessing the Aging Effect on Ti/Au Bilayers for Transition-Edge Sensor (TES) Detectors.

Transition-edge sensor (TES) microcalorimeters are advanced cryogenic detectors that use a superconducting film for particle or photon detection. We are establishing a new production line for TES detectors to serve as cryogenic anticoincidence (i.e., veto) devices. These detectors are made with a superconducting bilayer of titanium (Ti) and gold (Au) thin films deposited via electron beam evaporation in a high vacuum condition on a monocrystalline silicon substrate. In this work, we report on the development of such sensors, aiming to achieve stable sensing performance despite the effects of aging. For this purpose, patterned and non-patterned Ti/Au bilayer samples with varying geometries and thicknesses were fabricated using microfabrication technology. To characterize the detectors, we present and discuss initial results from repeated resistance-temperature (R-T) measurements over time, conducted on different samples, thereby augmenting existing literature data. Additionally, we present a discussion of the sensor's degradation over time due to aging effects and test a potential remedy based on an easy annealing procedure. In our opinion, this work establishes the groundwork for our new TES detector production line.

Inverse Spin-Hall Effect and Spin Swapping in Spin-Split Superconductors.

When a spin-splitting field is introduced to a thin film superconductor, the spin currents polarized along the field couples to energy currents that can only decay via inelastic scattering. We study spin and energy injection into such a superconductor where spin-orbit impurity scattering yields inverse spin-Hall and spin-swapping currents. We show that the combined presence of a spin-splitting field, superconductivity, and inelastic scattering gives rise to a strong enhancement of the ordinary inverse spin-Hall effect, as well as unique inverse spin-Hall and spin-swapping signals orders of magnitude stronger than the ordinary inverse spin-Hall signal. These can be completely controlled by the orientation of the spin-splitting field, resulting in a long-range charge and spin accumulations detectable much further from the injector than in the normal state. While the enhanced inverse spin-Hall signals offer a major improvement in spin detection sensitivity, the unique spin-swap signals can be utilized for designing devices where both the spin and current directions are controlled and altered throughout the geometry.

Passive bandpass filters for modern microwave communication systems

Background. Bandpass filters are an integral part of any radio engineering systems and modern communication systems. Research and development of new passive components is due to growing need for such elements for modernization and creation of new modern communication systems.
 Aim. A brief overview of passive bandpass filters. Their classification according to the type of implementation is given.
 Methods. Results of experimental research and design of different passive bandpass filters are considered.
 Results. Lumped elements filters, microstrip filters, filters on high-temperature superconductor films, filter on dielectric resonators, surface acoustic wave filters, bulk acoustic wave filters are considered. At a qualitative level, the main advantages and disadvantages are considered from point of view of electrical parameters and size indicators. Examples of topological and constructive implementation are given.
 Conclusion. The passive bandpass filters considered in the paper make it possible to implement frequency selection devices at operating frequencies up to 6 GHz and higher, taking into account modern system trends and requirements for devices of this type.

A Simple Model for the Induction Current Distribution in a Thin Superconducting Film

A Simple Model for the Induction Current Distribution in a Thin Superconducting Film

Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on α-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of α-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter-wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0 × 106 in the single photon region. The Qi of most devices are higher than 2.0 × 106. Moreover, most of them are still over 1 × 106 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability.

Ultrathin Limit on the Anisotropic Superconductivity of Single-Layered Cuprate Films

Exploring dimensionality effects on cuprates is important for understanding the nature of high-temperature superconductivity. By atomically layer-by-layer growth with oxide molecular beam epitaxy, we demonstrate that La2–x Sr x CuO4 (x = 0.15) thin films remain superconducting down to 2 unit cells of thickness but quickly reach the maximum superconducting transition temperature at and above 4 unit cells. By fitting the critical magnetic field (μ 0 H c2), we show that the anisotropy of the film’s superconductivity increases with decreasing film thickness, indicating that the superconductivity of the film gradually evolves from weak three- to two-dimensional character. These results are helpful to gain more insight into the nature of high-temperature superconductivity with dimensionality.

In-field electro-magnetic-force characteristics of high-temperature superconducting films containing cracks

Superconducting materials have so far been applied in the fields of superconducting motors, flux pumps and nuclear magnetic resonance, but they are prone to mechanical damage due to their material properties. In this paper, the influences of different crack types (including position, angle, size, quantity and spacing) on the characteristics of current-carrying and excited superconducting thin films are analyzed by numerical simulations, as well as their electromagnetic and mechanical characteristics. Several novel and important conclusions are found. In both states, the boundary crack presents the largest current density concentration, while the central crack produces the largest stress concentration. With the increase of crack spacing, the current density on the multi-crack film decreases and eventually tends to be stable. In the current-carrying state, compared with 3 mm cracked film, the current density of 1 mm cracked film is reduced by up to 62.5 %. The von Mises stress of high-temperature superconducting film with 0.1 mm single-spacing cracks is 22.5 % higher than that for 0.3 mm double-spacing cracks, which indicates that close spacing and a high number of crack types are most detrimental to the mechanical properties of high-temperature superconducting films. In the excited state, when the crack angle θ is 90°, the current density streamlines cannot be segmented effectively, which results in the current distribution trend closer to the defect-free film. A large amount of induced current flows into the low-flux region at the 3 mm crack, leading to an increased risk of film quench. The films with 1 mm single-spacing and double-spacing cracks form a low-flux region between the cracks, which makes the magnetic field more difficult to penetrate.

Deposition of Superconducting Nb3Sn Coatings Using Multiple Magnetron Sputtering Techniques

This paper describes the elemental and phase composition, microstructure, and superconducting properties of Nb3Sn deposited by magnetron sputtering. The films were deposited on sapphire substrates using three different techniques: co-evaporation, layer-by-layer deposition of Nb and Sn, and sputtering of a stoichiometric Nb3Sn target. The influence of magnetron operation mode on the as-deposited film element composition is described. After high-temperature annealing at 700–900 °C, the results indicate the formation of superconductive films. The highest critical temperature of 16.9 K was obtained for the film deposited at a stoichiometric Nb3Sn target and annealed at a temperature of 800 °C for 12 h. These results could be used for superconducting radio-frequency applications.

Gauge Theories of Josephson Junction Arrays: Why Disorder Is Irrelevant for the Electric Response of Disordered Superconducting Films

We review the topological gauge theory of Josephson junction arrays and thin film superconductors, stressing the role of the usually forgotten quantum phase slips, and we derive their quantum phase structure. A quantum phase transition from a superconducting to the dual, superinsulating phase with infinite resistance (even at finite temperatures) is either direct or goes through an intermediate bosonic topological insulator phase, which is typically also called Bose metal. We show how, contrary to a widely held opinion, disorder is not relevant for the electric response in these quantum phases because excitations in the spectrum are either symmetry-protected or neutral due to confinement. The quantum phase transitions are driven only by the electric interaction growing ever stronger. First, this prevents Bose condensation, upon which out-of-condensate charges and vortices form a topological quantum state owing to mutual statistics interactions. Then, at even stronger couplings, an electric flux tube dual to Abrikosov vortices induces a linearly confining potential between charges, giving rise to superinsulation.

A process for the preparation of high-quality and uniform large-scale Bi2212 superconducting films via the sol-gel method

Bi2212 high-temperature superconducting films (HTSFs) have garnered significant interest as a potential material for the development of high-Tc microwave and terahertz (THz) devices due to their intrinsic Josephson effect. This work presents the utilization of the polyvinyl pyrrolidone (PVP) -assisted sol-gel dip coating (PSGDC) method for the large-scale production of Bi2212 HTSFs. Initially, Bi2212 HTSFs were prepared on a small-scale single crystal (001)-oriented SrTiO3 substrates, and comprehensive characterization of their phase purity, crystal structure, surface morphology, microstructure, stress state, and transport properties was conducted as a foundation for further analysis. By optimizing the crystallization conditions and PVP content, the Bi2212 HTSF achieved improved performance, including a higher onset superconducting transition temperature (Tc, onset) of 94 K, zero-resistance temperature (Tc, zero) of 86 K, and a critical current density (Jc) of 6.8 × 104 A/cm2 under a zero magnetic field at 2 K. Subsequently, the optimized process was applied to successfully prepare a large-scale Bi2212 HTSF with a diameter of 50 mm, exhibiting uniform phase composition, surface morphology, and superconducting properties, expanding the potential applications of Bi2212 HTSFs.

Multi-channel angular selective window based on the epsilon-near-zero features of YaBa2Cu3O7 material and photonic crystals ceramic structure of extremely small dispersion edge regions

In this paper, the investigation of the angular selective windows (ASWs) is realized by constructing multilayer ceramic photonic crystals 1 (MCPC1) containing superconductor films YaBa2Cu3O7 and air layers, MCPC2 composed of dielectrics layers of gallium arsenide ceramic (GaAs), silicon dioxide (SiO2), and aluminium nitride ceramic (AIN), and MCPC3 made up of GaAs and SiO2 films. The epsilon-near-zero (ENZ) properties of the superconductor in MCPC1 and the extremely small dispersion edge regions (DERs) in MCPC2 and MCPC3 provide criteria for angle selection. Organic combinations of three MCPCs can be used to achieve single-channel, dual-channel, three-channel, and four-channel ASWs. At the same time, the applicable working frequency bands for various channels are also studied. In particular, thanks to the lossless ENZ characteristics of YaBa2Cu3O7, ultra-wideband single-channel ASWs of 220–1500 THz can be realized. In addition, the temperature change is also conducive to the control of ASWs position. As far as we know, there are few reports on the channel of ASWs at present, so we hope that the proposed design method will be beneficial to the research of improving the angular device.

Characterization of NbTiN Films With Thicknesses Below 20 nm for Low Power Kinetic Inductance Amplifiers

A quantum-limited amplification chain is a fundamental advantage for any application that may benefit from the detection of very faint signals. Reading out arrays of superconducting detectors (TESs or MKIDs), resonant cavities, or qubits, calls for large bandwidth amplifiers in addition to having the lowest possible noise. At millikelvin temperatures, Kinetic Inductance Traveling-Wave Parametric Amplifiers (KI-TWPAs) working in 3-way-mixing (3WM) and fabricated from a 20 nm thick NbTiN film have shown promising noise performances, as they can operate close to the quantum limit [1]. However, they still require fairly high pump power. Devices that would require lower pump power would be easier to implement in readout chains, could reach the quantum limit and they would be compatible with qubit readout. A possible solution for obtaining this optimal configuration is to use a thinner superconducting film. In this work we explore the properties of NbTiN films with a thickness less than 20 nm and we report the obtained experimental characterizations in terms of critical temperature, normal resistivity, and kinetic inductance. A new design for a 3WM KI-TWPA amplifier, based on these developed superconducting films, is introduced and discussed.

Comment on "Anisotropic Scattering Caused by Apical Oxygen Vacancies in Thin Films of Overdoped High-Temperature Cuprate Superconductors".

Comment on "Anisotropic Scattering Caused by Apical Oxygen Vacancies in Thin Films of Overdoped High-Temperature Cuprate Superconductors".

Van der Waals Self-Epitaxial Growth of Inch-Sized Superconducting Niobium Diselenide Films.

Ultrathin superconducting films are the basis of superconductor devices. van der Waals (vdW) NbSe2 with noncentrosymmetry exhibits exotic superconductivity and shows promise in superconductor electronic devices. However, the growth of inch-scale NbSe2 films with layer regulation remains a challenge because vdW structural material growth is strongly dependent on the epitaxial guidance of the substrate. Herein, a vdW self-epitaxy strategy is developed to eliminate the substrate driving force in film growth and realize inch-sized NbSe2 film growth with thicknesses from 2.1 to 12.1 nm on arbitrary substrates. The superconducting transition temperature of 5.1 K and superconducting transition width of 0.30 K prove the top homogeneity and quality of superconductivity among all of the synthetic NbSe2 films. Coupled with a large area and substrate compatibility, this work paves the way for developing NbSe2 superconductor electronics.

Topotactic fabrication of transition metal dichalcogenide superconducting nanocircuits

Superconducting nanocircuits, which are usually fabricated from superconductor films, are the core of superconducting electronic devices. While emerging transition-metal dichalcogenide superconductors (TMDSCs) with exotic properties show promise for exploiting new superconducting mechanisms and applications, their environmental instability leads to a substantial challenge for the nondestructive preparation of TMDSC nanocircuits. Here, we report a universal strategy to fabricate TMDSC nanopatterns via a topotactic conversion method using prepatterned metals as precursors. Typically, robust NbSe2 meandering nanowires can be controllably manufactured on a wafer scale, by which a superconducting nanowire circuit is principally demonstrated toward potential single photon detection. Moreover, versatile superconducting nanocircuits, e.g., periodical circle/triangle hole arrays and spiral nanowires, can be prepared with selected TMD materials (NbS2, TiSe2, or MoTe2). This work provides a generic approach for fabricating nondestructive TMDSC nanocircuits with precise control, which paves the way for the application of TMDSCs in future electronics.