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Over the past decades, superconducting qubits have emerged as one of the leading hardware platforms for realizing a quantum processor. Consequently, researchers have made significant effort to understand the loss channels that limit the coherence times of superconducting qubits. A major source of loss has been attributed to two level systems that are present at the material interfaces. It is recently shown that replacing the metal in the capacitor of a transmon with tantalum yields record relaxation and coherence times for superconducting qubits, motivating a detailed study of the tantalum surface. In this work, the chemical profile of the surface of tantalum films grown on c‐plane sapphire using variable energy X‐ray photoelectron spectroscopy (VEXPS) is studied. The different oxidation states of tantalum that are present in the native oxide resulting from exposure to air are identified, and their distribution through the depth of the film is measured. Furthermore, it is shown how the volume and depth distribution of these tantalum oxidation states can be altered by various chemical treatments. Correlating these measurements with detailed measurements of quantum devices may elucidate the underlying microscopic sources of loss. [ABSTRACT FROM AUTHOR]

Background: Kinetic Inductance Travelling Wave Parametric Amplifiers (KITWPAs) are a variant of superconducting amplifier that can potentially achieve high gain with quantum-limited noise performance over broad bandwidth, which is important for many ultra-sensitive experiments. In this paper, we present a novel modelling technique that can better capture the electromagnetic behaviour of a KITWPA without the translation symmetry assumption, allowing us to flexibly explore the use of more complex transmission line structures and better predict their performance. Methods: In order to design a KITWPA with optimal performance, we investigate the use of different superconducting thin film materials, and compare their pros and cons in forming a high-gain low-loss medium feasible for amplification. We establish that if the film thickness can be controlled precisely, the material used has less impact on the performance of the device, as long as it is topologically defect-free and operating within its superconducting regime. With this insight, we propose the use of Titanium Nitride (TiN) film for our KITWPA as its critical temperature can be easily altered to suit our applications. We further investigate the topological effect of different commonly used superconducting transmission line structures with the TiN film, including the effect of various non-conducting materials required to form the amplifier. Results: Both of these comprehensive studies led us to two configurations of the KITWPA: 1) A low-loss 100 nm thick TiN coplanar waveguide amplifier, and 2) A compact 50 nm TiN inverted microstrip amplifier. We utilise the novel modelling technique described in the first part of the paper to explore and investigate the optimal design and operational setup required to achieve high gain with the broadest bandwidth for both KITWPAs, including the effect of loss. Conclusions: Finally, we conclude the paper with the actual layout and the predicted gain-bandwidth product of our KITWPAs.

We have modeled the effects of self-field on the critical current density $\boldsymbol{J_\text{c}}$ in high temperature superconducting REBCO tapes, by considering them as a collection of Josephson junctions (JJs) in parallel. We have used a 2D JJ framework for each junction and included their component self-field effects using the well known expression for the magnetic field produced by a thin strip. We provide computational and analytic expressions for the spatial distribution of $\boldsymbol{J_\text{c}}$ , enabling us to calculate the critical current of coated conductors over the whole field range. We find that $\boldsymbol{J_\text{c}}$ in self field for thin tapes is broadly independent of the width but strongly dependent on the thickness of the tape. For example, if a tape thickness is doubled, even if $\boldsymbol{J_\text{c}}$ is unchanged in high field, we expect the self-field $\boldsymbol{J_\text{c}}$ to drop by $\sim \!20 \,\%$ because of the larger self-field produced. Our results are compared to experimental results for technological coated conductors from the literature and good agreement is found. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) has been identified as a promising growth method for high-uniformity superconducting thin films for superconducting quantum photonic applications, offering superior uniformity, thickness control and conformality to techniques such as reactive sputtering. The potential scalability of ALD makes this method especially appealing for fabrication of superconducting nanowires and resonators across large areas. We report on the growth of highly uniform superconducting NbN thin films via plasma-enhanced atomic layer deposition (PEALD) with radio frequency substrate biasing, on a 200 mm (8 inch) Si wafer, specifically for superconducting nanowire single-photon detector applications. Niobium nitride films were grown using (tert-butylimido)-tris(diethylamido)-niobium(V) precursor and an H _2 /Ar plasma. The superconducting properties of a variable thickness series of films (5.9–29.8 nm) show critical temperature ( T _c ) of 13.5 K approaching bulk thickness (28.8 nm) with low suppression down to the ultrathin regime (5.9 nm), with T _c = 10.2 K. T _c across the 200 mm wafer with 8 nm thick NbN, measured in 15 mm intervals, exhibits minimal variation ( 10 MA cm ^−2 at 2.6 K. PEALD could therefore be a pivotal technique in enabling large-scale fabrication of integrated quantum photonic devices across a variety of applications.

We present our studies on the evolution of the normal and superconducting properties with thickness of thin Nb films with a low level of non-magnetic disorder (kFl ≈ 150 for the thickest film in the set). The analysis of the superconducting behavior points to the presence of magnetic moments, hidden in the native oxide on the surface of Nb films. Using the Abrikosov-Gorkov theory, we obtain the density of surface magnetic moments of 1013  cm−2, which is in agreement with the previously reported data for Nb films. [ABSTRACT FROM AUTHOR]

Pulsed lasers were used to drill small holes distributed homogeneously on buffer layers of coated conductors, aiming at improving their mechanical properties. Each hole should be engraved by only one pulse of laser for practicality. The effect of pulsed laser engraving on buffer layers, CeO2 in this study, were investigated. The size and depth of the hole can be controlled by adjusting laser parameters. REBa2Cu3Oy (REBCO) layers were then grown on the laser patterned buffer. The growth mechanism of REBCO above the drilled holes was studied. In addition, influence of drilled holes on the critical currents of coated conductors were studied. Finally, the effect on mechanical strength of as grown samples were studied by measuring their delamination strength under transverse tension. [ABSTRACT FROM AUTHOR]

Manufacturing of coated conductors can be tailored for future use operating parameters, such as high temperature and low field, mid temperature and mid field and low temperature and high field. Different methods of flux pinning are being tested world-wide to enhance critical currents of high temperature superconductor yttrium barium copper oxide coated conductors for these various operating conditions. Magnetic materials are interesting to consider as flux pinning additions because of their potential for very strong pinning strength. This research describes the study of different magnetic phase additions to superconducting thin films, including: BaFe12O19, La0.67Ca0.33MnO3, Y3Fe5O12, and SrRuO3. Nano-size additions with volume percent ranging from 0.5% to 5% were incorporated by utilizing pulsed laser deposition to form alternating layers of magnetic dopants and yttrium barium copper oxide to minimize degradation of Tc. Experimental critical current density (Jcm(H,T)) results for mid temperature (30 K–65 K) / mid field (1 T–5 T) and low temperature (<30 K) / high field (>5 T) and microstructural TEM are presented. Results illustrate the benefits and interplay of combining magnetic flux pinning and core pinning by the magnetic additions and associated film defects, and suggest applications suitable for each system studied. [ABSTRACT FROM AUTHOR]

The recent realisations of hydrogen doped LnFeAsO (Ln = Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density Jc. The superconducting transition temperature Tc is comparable to NdFeAs(O,F). Transmission electron microscopy investigation supported that hydrogen is homogenously substituted for oxygen. A high self-field Jc of over 10 MA/cm2 was recorded at 5 K, which is likely to be caused by a short London penetration depth. The anisotropic Ginzburg–Landau scaling for the angle dependence of Jc yielded temperature-dependent scaling parameters γJ that decreased from 1.6 at 30 K to 1.3 at 5 K. This is opposite to the behaviour of NdFeAs(O,F). Additionally, γJ of NdFeAs(O,H) is smaller than that of NdFeAs(O,F). Our results indicate that heavily electron doping by means of hydrogen substitution for oxygen in LnFeAsO is highly beneficial for achieving high Jc with low anisotropy without compromising Tc, which is favourable for high-field magnet applications. [ABSTRACT FROM AUTHOR]

The higher order resonances of microwave superconducting filters with spiral resonators were suppressed, giving a very wide stop‐band. In one filter spirals were modified to have equal fundamental resonances, but different higher order resonances, by adding stubs and using non‐uniform line width. The higher resonances were reduced to −39 dB, in a stop band up to 4.3 times the pass band centre. In another filter, parasitic resistive resonators were added, suppressing the responses to −57 dB. The resistance is provided by patterning the 200 nm gold overlay already required for the external contacts. The increase in pass band loss is not measurable. Measurements of a single spiral resonator with a gold‐YBCO bi‐layer (200 and 600 nm respectively) suggest that the resistivity of the gold layer at 15 K is the order of 22 times that of bulk gold, a slight advantage for the present application. At 100 K, it is about double. [ABSTRACT FROM AUTHOR]

Trapped-flux magnets made of stacks of superconducting tapes are an interesting and important alternative to the application of rare-earth permanent magnets and trapping flux in bulk superconductors. Many applications, such as electric motors, can require the complex shapes of magnetic elements to combat issues such as demagnetization during the operation. Therefore, a reliable production technique of high temperature superconductor (HTS) stacks with different geometries is required to meet the needs of industry. In this article, a method of shaping the epoxy-glued stacks of superconducting tapes is proposed and investigated. The application of hot press allows to easily change the shape of the stack. The influence of shaping the stack on the density of trapped magnetic flux as well as critical current are presented. Experimental and numerical analyses are performed and their results are matched to find the change in the superconducting properties of the tapes. They show that with the proper process parameters the stacks can be shaped with only minor decrease of performance. However, strong degradation is observed if the applied force is too high. The observed problems are discussed and the possible solutions are proposed. [ABSTRACT FROM AUTHOR]

Long standing data from niobium thin-film accelerating cavities will be revisited and analyzed by a modified London model of radio-frequency (RF) superconductivity. First, the applicability of this model is explored using the data of the Bardeen–Cooper–Schrieffer (BCS) surface resistance and its dependence on the RF magnetic field, temperature, and mean free path. Second, the RF losses from the trapped magnetic flux are analyzed with regard to their dependence on these same parameters. [ABSTRACT FROM AUTHOR]

This article puts forward a method based on high-temperature superconducting (HTS) current limiting technology, to improve the overcurrent stability for a battery unit in a superconducting magnetic energy storage (SMES)-battery hybrid energy storage systems (HESS). In contrast to supercapacitors, flywheels and other energy storage systems, SMES-battery HESS possess the technical properties of power capacity, energy, and response speed, among others. Thus, SMES-battery HESS may be utilized to handle power swing, energy transfer, voltage fluctuation, and related transient stability issues. But an overcurrent in a battery unit is harm to its cycle life of the battery. Hence, the internal protection system of the battery unit is used to remove a fault by cutting off its outputs. In this article, a YBa2Cu3O7-X (YBCO) thin film is employed as the protection device to limit the overcurrent in a battery unit. In normal operation, the thin film is in the superconducting state, and its influence on the system can be ignored. An overcurrent will be limited evidently lower than the action threshold of the internal protection system by the quench resistance of the thin film. Therefore, the whole outputs of a battery unit will not be interrupted and restarted. Through the verification experiment carried out in our laboratory, the proposed protection method operated as expected, and the stability, as well as the reliability of the battery unit, could be improved. [ABSTRACT FROM AUTHOR]

The influence of technological parameters (composition of precursor powders, type of additions, temperature, and pressure) on the superconducting characteristics (transition temperature, critical current density, and critical magnetic fields) of MgB2-based materials (bulk, wires, and thin films) and the correlation with their microstructure were studied. Microstructural observations are in good agreement with ab-initio modeling. The X-ray, Auger spectroscopy, and SEM EDX study show that impurity oxygen and carbon (possibly as dopant) are present in the magnesium diboride structure. The elements are distributed inhomogeneously, thus creating the nanostructure (which can be purposefully changed by manufacturing conditions) responsible for flux pinning and other SC characteristics. [ABSTRACT FROM AUTHOR]

The superconducting transition temperature of 140 nm ± 10 nm thin films on sapphire substrates, which were deposited by magnetron sputtering, was around 36 K. Using a magnetization technique, the film's critical current density was estimated as JC = 1.8 × 107 А/cm2 at 10 K, JC = 8 × 106 А/m 2 at 20 K in a zero magnetic field B, and JC = 3 × 106 А/m2 at 10 K and B = 5 T. The values of the upper critical magnetic field Bc2 and the irreversibility field Birr estimated using the four-probe technique were BC2(22 K) = 15 T when H||film surface, 11 T when H⊥film surface, and Birr(22 K) = 11 T when H||film surface. The X-ray study showed that the microstructure of the film contains only MgB2 and MgO (in minority). The SEM and EPXMA study and quantitative Auger spectroscopy analysis revealed periodical variations of the film composition on the nanolevel and the presence of (mainly) two intercalated Mg-B-O-C phases of slightly different, especially in oxygen content, and thus with different conductivity and, possibly, with different TC. The characteristics of superconducting magnesium diboride films make them promising for application in electronic devices, e.g., as high-pass filters. [ABSTRACT FROM AUTHOR]

In a superconducting photon detector, the effective transition to the normal state can be induced by the instability of the flux flow regime. Indeed, in the presence of self-magnetic field, the local suppression of superconductivity induced by photon absorption determines vortex nucleation and flux flow regime, which can make the superconducting state unstable. Understanding such instability can boost the performances of those superconducting devices based on this resistive switching. Here, we present the study of the geometry influence on such instability in NbN and NbTiN ultrathin films. Despite the same patterned microbridge geometry, the two superconductors show different behaviors at very low applied magnetic fields. A comparison with other superconductors outlines the possibility to tune the resistive switching by geometry effects in interesting materials for devices applications. Finally, we also report the influence of the cooling environment on the electric critical power in superconducting thin films. [ABSTRACT FROM AUTHOR]

We investigate the feasibility of using the semiconductor InAs nanorods for flux pinning in Nb thin films. The InAs nanorods are grown in the vertical direction on Si (111) substrates by metal-organic chemical vapor deposition. The grown nanorods are about 80 nm in diameter, 5 μm in height, and 2 × 109/cm2 in density. The four-terminal strip pattern of Nb films is fabricated on nanorod-grown substrates and, for the reference, on nanorodfree substrates by sputtering through a metal mask. We observe clear enhancement of the upper critical fields and the critical current densities for field oriented along the nanorod axis in the Nb film with embedded nanorods. We also confirm the flux pinning by InAs nanorods in the measurements of the angular dependence of critical current densities. Our results indicate that the InAs nanorods are promising linear defects for flux pinning research in superconductors. [ABSTRACT FROM AUTHOR]

Superconducting titanium thin films are good candidates for transition edge sensors. In this paper, we deposit titanium thin films on cooled silicon-on-insulator substrates by using electron-beam evaporation. The deposition rate dependence of the film stress, resistivity, and superconducting transition temperature are presented and analyzed. The relationship between film electrical properties and thickness is discussed. For investigating the heating influence on thin Ti films, a depth profile of oxygen diffusion in the films is also analyzed by X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

To connect superconducting wires through a different superconductor, it is essential to evaluate a range of characteristics of the various superconducting materials. In this study, a combination of YBa2Cu3 O7-δ (YBCO) and La1.85Sr0.15CuO4 (LSCO), which are typical high-temperature superconductors, was investigated. An LSCO/YBCO layered thin film (LSCO/YBCO bilayer) was prepared and its crystallinity, surface morphology, and electrical properties were evaluated. The LSCO thin film grew epitaxially, oriented to the (00l) plane on the (00l)-oriented YBCO thin film due to the small lattice mismatch between YBCO and LSCO. The surface flatness of the LSCO/YBCO bilayer was almost the same as that of the LSCO thin film, because the LSCO thin film grew without roughening the surface of the YBCO thin film. The electrical resistivity of the LSCO/YBCO bilayer decreased at the individual superconducting-transition temperatures of YBCO and LSCO, and eventually became superconducting at 20 K. The superconducting properties of YBCO and LSCO were almost preserved, with the result that a superconducting connection between YBCO and LSCO was achieved. [ABSTRACT FROM AUTHOR]

The CERN SRF infrastructure was originally set up for Nb on Cu-coated cavities for large electron positron collider (LEP) and later for large hadron collider (LHC). Today, Superconducting RF has become a vital technology not only for LHC but also for high intensity and energy upgrade of isotope separator on line device (HIE-ISOLDE) and the high luminosity (HL)-LHC project. More superconducting cavities will be needed for a potential high energy (HE)-LHC or for any of the future circular collider options, which are currently under study. To meet these demands, CERN has improved its SRF infrastructure over the recent years and has started several R&D lines including improved thin film coating techniques, high-power couplers, cold-test diagnostics, etc. This paper will give an overview of CERN's SRF activities today, and the challenges of future projects. [ABSTRACT FROM AUTHOR]

The (CuTl)BaCaCuO thin films were synthesized at 895, 905 and 920 °C. These films are c-axis oriented and have shown tetragonal structure. The samples have been investigated for excess conductivity analysis. The analyses are carried out by following Aslamazov-Larkin theory. It is observed that the values of ξ, v, λ, J decrease, but that of B(T), B(T), J(0) increase with the increase of synthesis temperature. However, with the post-annealing of the samples at 100, 300 and 400 °C, the values of ξ(0), v, τ and J increase but, the values of B(T), B(T) and J(0) suppress with the increasing annealing temperature. It is proposed that with the higher synthesis temperature thallium defects are created in the charge reservoir layer that act as pinning centers whereas with post-annealing of the samples oxygen defects are removed. The former enhances whereas the later promotes suppression of B(T), B(T), J(0) parameters in (CuTl)BaCaCuO thin films. [ABSTRACT FROM AUTHOR]

Superconductors can get unstable in the applications due to its thermomagnetic instability characteristics. Superconducting thin films, fabricated by either the pulsed laser deposition or chemical evaporation, usually show nonhomogeneous or granular microstructures. Thus, nonhomogeneous distribution of the superconducting properties is intrinsically introduced into the thin films. In this paper, we study the flux avalanche behaviors of the nonhomogeneous/granular MgB2 thin films under applied magnetic field by numerically solving the coupled nonlocal and nonlinear thermomagnetic equations. The influences of the grain sizes and thickness of the channels between islands on the propagation paths of the dendritic flux avalanches are considered in the simulation. It is found that the flux avalanches preferentially propagate along the channels, and the smaller the critical current density inside the channel the more avalanches propagate along it. The numerical simulation results are consistent with the experimental results. In addition, we have investigated the effect of environment temperature and magnetic field ramp rate on the flux avalanche behaviors of nonhomogeneous MgB2 thin films. Our results may be beneficial to the design and real application of the thin film superconducting devices. [ABSTRACT FROM AUTHOR]

Atomically flat superconducting NbN thin films have been grown on the SrTiO3 (111) substrate by plasma-assisted molecular beam epitaxy for the first time. Using scanning tunneling microscopy and in situ reflection high energy electron diffraction, we investigate the surface structure of epitaxial NbN thin films on the SrTiO3 (111) substrate. The orientation (1011¯)NbN//(1122¯)STO is dominating at substrate temperature above 700 °C. The quality of the as-grown films can be further improved by annealing at elevated temperatures. The homogeneous spatial distribution of superconducting gaps and magnetic vortices further demonstrates the high quality of the NbN films. [ABSTRACT FROM AUTHOR]

A fabrication process for NbN films with a high transition temperature (TC) of about 17 K was developed to realize NbN/AlN/NbN superconducting-tunnel-junction array particle detectors with a high operation temperature of >1 K and a high sensitivity by using atomic layer deposition (ALD). The source (precursor) of the NbN films was (tert -butylimido)bis(diethylamino)niobium [C16H39N4Nb]. NbN films were deposited on M-plane sapphire wafers. A 50-nm-thick NbN film was deposited with a substrate temperature of about 570 K and exhibited a (TC) of 12.35 K. To improve the superconducting properties of the NbN formed by ALD, a postdeposition rapid thermal annealing process was performed. The dependence of (TC), the surface morphology, and the crystallinity of the film on thermal annealing temperatures was evaluated. [ABSTRACT FROM PUBLISHER]

In superconducting single-photon detectors (SSPD), the efficiency of local suppression of superconductivity and hot-spot formation is controlled by diffusivity and electron–phonon interaction time. Here, we selected a material, 3.6-nm-thick MoN${}_{x}$ film, which features diffusivity close to those of NbN traditionally used for SSPD fabrication, but with electron–phonon interaction time an order of magnitude larger. In MoN${}_{x}$ detectors, we study the dependence of detection efficiency on bias current, photon energy, and strip width, and compare it with NbN SSPD. We observe nonlinear current-energy dependence in MoN ${}_{x}$ SSPD and more pronounced plateaus in dependences of detection efficiency on bias current, which we attribute to longer electron–phonon interaction time. [ABSTRACT FROM PUBLISHER]

We investigated the suitability of AlN as a buffer layer for NbN superconducting nanowire single-photon detectors (SNSPDs) on GaAs. The NbN films with a thickness of 3.3–20 nm deposited onto GaAs substrates with an AlN buffer layer demonstrate a higher critical temperature, critical current density, and lower residual resistivity in comparison to films deposited onto bare substrates. Unfortunately, the thermal coupling of the NbN film to the substrate weakens. SNSPDs made of 4.9-nm-thick NbN films on buffered substrates (in comparison to detectors made from NbN films on bare GaAs) demonstrate three orders of magnitude lower dark count rates and about ten times higher detection efficiency at 900 nm being measured at 90% of the critical current. The system timing jitter of SNSPDs on buffered substrates is 72 ps, which is 36 ps lower than those on bare substrate. However, a weaker thermal coupling of NbN nanowire to the buffered substrate leads to a latching effect at bias currents > 0.97 I C. [ABSTRACT FROM PUBLISHER]

Vertically aligned nanocomposite (VAN) ( La 0.7 Sr 0.3 MnO 3 ) 0.5 (CeO 2 ) 0.5 and pure La 0.7 Sr 0.3 MnO 3 layers were incorporated into YBa 2 Cu 3 O 7−δ (YBCO) thin films as bilayer stacks for magnetic flux pinning enhancement. The films show high epitaxial quality, suggested by XRD and TEM study. The critical temperature T c of the bilayers is about 90 K, which is close to that of pure YBCO films, while both the self-field J c sf and in-field critical current density J c in-field are largely enhanced. Among all samples, the film with VAN cap layer shows the highest J c values in all field ranges. This study demonstrates an effective way towards the tunable pinning effect for YBCO coated conductors by both defect and magnetic pinning. [ABSTRACT FROM AUTHOR]

We discuss calibration issues in wideband (2–20 GHz) surface impedance measurements in a cryogenic and high magnetic field environment. We show that, in the case of measurements taken on superconducting thin films, the substantial impossibility of a full, three-standard calibration can be partially overcome by exploiting appropriate approximations and the basic properties of superconductors. We discuss a modification of the so-called short-only calibration, in order to increase the accuracy of the measurements. We relate the material properties of a sample under study to the measured surface impedance, which is affected by the geometry of the measurement, and we discuss the effects on the proposed approximate calibration procedure. We experimentally check the applicability of the approximations at the ground of the method, and we thoroughly discuss the uncertainties related to the approximations employed. Finally, we report the sample measurements of the surface impedance of two MgB2 superconducting films. [ABSTRACT FROM AUTHOR]

It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (~10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4X higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 X 1015 cm-2 (the average volume density of 1.7 X 1021 cm-3), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials. [ABSTRACT FROM AUTHOR]

The epitaxial thin films of electron-doped infinite-layer cuprate superconductor Sr1-xLaxCuO2 (SLCO; $x = 0.1$ ) were grown by dc magnetron sputtering, and their structural and electrical properties were systematically investigated by changing mismatch to substrate and SLCO film thickness, with a reduction annealing period under vacuum to remove the excess apex oxygen. Thin films of BaySr1−yTiO3 (BSTO) with y = 0.55$ , 0.6, and 0.7, prepared on (001) (La0.18Sr0.82)(Al0.59Ta0.41)O3 substrates, were used as the epitaxial buffer layers to induce different levels of tensile strain in c$ -axis-oriented SLCO, while (001) LaAlO3 substrates were used for the growth of a value of c$ -axis oriented SLCO was obtained on the BSTO ( y = 0.6$ ) layers and the mismatch dependence of strain relaxation thickness was clarified. The strain in a was obtained in the $a$ -axis SLCO for the first time. Based on these results, the strain effects of the SLCO film properties are discussed. [ABSTRACT FROM AUTHOR]

Amorphous superconductors have become attractive candidate materials for superconducting nanowire single-photon detectors due to their ease of growth, homogeneity and competitive superconducting properties. To date the majority of devices have been fabricated using WxSi1-x, though other amorphous superconductors such as molybdenum silicide (MoxSi1-x) offer increased transition temperature. This study focuses on the properties of MoSi thin films grown by magnetron sputtering. We examine how the composition and growth conditions affect film properties. For 100 nm film thickness, we report that the superconducting transition temperature (Tc) reaches a maximum of 7.6 K at a composition of Mo83Si17. The transition temperature and amorphous character can be improved by cooling of the substrate during growth which inhibits formation of a crystalline phase. X-ray diffraction and transmission electron microscopy studies confirm the absence of long range order. We observe that for a range of 6 common substrates (silicon, thermally oxidized silicon, Rand C-plane sapphire, x-plane lithium niobate and quartz), there is no variation in superconducting transition temperature, making MoSi an excellent candidate material for SNSPDs. [ABSTRACT FROM AUTHOR]

To date, magnetic shields utilizing high-temperature superconductor materials mostly comprise bulk materials, usually shaped into a cylinder and then heat treated. We analyze the potential of thin-film technology, whereby a layer of superconductor is deposited on a substrate, to fabricate magnetic shields. Films deposited on a curved surface are inevitably granular, leading to reduced critical current density compared with crystalline films. This limits the maximum field that can be screened. Granular films also have an enhanced penetration depth compared with the bulk value, which determines the maximum possible screening at applied fields below the maximum. We demonstrate the utility of a mutual inductance measurement to evaluate small flat test samples of a granular film for their potential as a shielding material in a more complex geometry. This measurement predicts both the maximum magnetic field that can be screened and the residual leakage at fields below the maximum. The tested film was produced by the Electrophoretic deposition of YBCO on a silver substrate. The maximum screening field was comparable with that obtained for a similar film on a cylindrical substrate. We also show comparable results from a crystalline YBCO film. [ABSTRACT FROM PUBLISHER]

Transition-edge sensors (TESs) are very versatile superconducting devices used to detect radiation from gamma-rays to visible and submillimeter. The intrinsic capability to measure the energy of the absorbed photons with very high energy resolution and the related possibility to resolve the number of incident photons distinguish photon-number resolving (PNR) devices from any other photon detectors. PNR detectors are fundamental for the measurement of the photon-number distribution of single-photon emitters and for the progress of quantum information technology and quantum metrology. By reducing the active area of TESs for visible-NIR light from typical values of 10^-10\ \m^2 toward 10^-12\ \m^2 and by increasing the TES operating temperature, we should be able to combine the high energy resolution permitted by very low heat capacity with fast response time. To support the future design and development of this new type of detector, in this work we compare experimental data with circuit simulation results based on the two-fluid theory. [ABSTRACT FROM PUBLISHER]

It is known that BaZrO and Ag can improve the magnetic and transport performance of YBCO thin film through totally disparate ways. BaZrO plays the role of flux pinning centers and Ag improves the transparency of the YBCO grain boundaries. However, similar research is rare on the fluorine-free derived YBCO films. In this research, BaZrO-doped, Ag-doped and BaZrO/Ag hybrid-doped YBCO films were synthesized through a fluorine-free metal-organic deposition method. BaZrO was found to deteriorate the microstructure and performance of YBCO, while Ag-doping was found to enhance the crystallization of YBCO and resulted in a high Jc of 3.87 MA/cm in self-field at 77 K. However, the microstructure and performance of the BaZrO/Ag hybrid-doped YBCO film showed that the positive impact of Ag-doping was totally overwhelmed by that of BaZrO. [ABSTRACT FROM AUTHOR]

The c-axis orientation YBa2Cu3Oδ thin film was prepared directly on MgO substrate by the pulse laser deposition. The thickness of the film is 170 nm. The superconducting critical temperature is Tc50% = 87:5 K and the width of superconducting transition is ΔT = 1:8 K. The temperature dependences of magnetoresistance were measured up to 90 kOe. The widths of the transition to the superconducting state versus applied magnetic field were derived and they were fitted using the formula: ΔT = CHm +ΔT0. The irreversibility fields as a function of temperature were obtained and fitted by the de Almeida and Thouless-like equation: Hirr = Hirr0(1-T=Tc0)n. The irreversibility field at the liquid nitrogen temperature was calculated and it is Hirr = 43:8 kOe when the applied magnetic field is parallel to the c-axis. [ABSTRACT FROM AUTHOR]

We report the determination of critical current density Jc flowing in YBa2Cu3O7-δ superconducting thin films by two independent criteria. The estimation of Jc was carried out by an inductive technique, i.e., the so-called screening technique. Both the imaginary part of the fundamental harmonic of susceptibility χ1" and the third harmonic of the voltage V3 criteria were used to determine the full penetration field. Our goal is to shed light on the selection of the criterion for the determination of Jc. In order to compare the inductive criteria, we investigated the homogeneity of Jc via transport measurements conducted on microbridges patterned in the films. Based on the transport method, we found that, for temperatures close to critical temperature Tc, both techniques yield similar results in the determination of Jc. However, at temperatures relatively far from Tc, the V3 criterion showed better agreement with the transport data. Furthermore, using both criteria, we propose an alternative methodology to estimate in situ the coil factor associated with the V3 criterion, avoiding in this way the need for implementing an additional technique. [ABSTRACT FROM PUBLISHER]

We present a detailed thermal and electrical model of superconducting transition edge sensors (TESs) connected to quasiparticle (qp) traps, such as the W TESs connected to Al qp traps used for CDMS (Cryogenic Dark Matter Search) Ge and Si detectors. We show that this improved model, together with a straightforward time-domain optimal filter, can be used to analyze pulses well into the nonlinear saturation region and reconstruct absorbed energies with optimal energy resolution. [ABSTRACT FROM AUTHOR]

MgB thin films were fabricated on r-plane AlO ( ${1} \overline{{1}} {0} {2})$ substrates. First, deposition of boron was performed by rf magnetron sputtering on AlO substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of FeO nanoparticles on the structural and magnetic properties of films, MgB films were coated with different concentrations of FeO nanoparticles by spin coating process. The magnetic field dependence of the critical current density J was calculated from the M-H loops and magnetic field dependence of the pinning force density, f( b), was investigated for the films containing different concentrations of FeO nanoparticles. The critical current densities, J, in 3T magnetic field at 5 K were found to be around 2·7 × 10 A/cm, 4·3 × 10 A/cm, 1·3 × 10 A/cm and 5·2 × 10 A/cm for films with concentrations of 0, 25, 50 and 100% FeO, respectively. It was found that the films coated with FeO nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by FeO became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by FeO nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material. [ABSTRACT FROM AUTHOR]

The authors report the successful fabrication of superconducting tantalum nitride (TaN) thin films using a pulsed laser deposition technique with 1064 nm radiation. Films with thickness ∼100 nm deposited on MgO (100) single crystals and on oxidized silicon (SiO2) substrates exhibited a superconducting transition temperature of ∼8 K and 6 K, respectively. The topography of these films were investigated using atomic force and scanning electron microscopy, revealing fairly large area particulate free and smooth surfaces, while the structure of the films were investigated using θ-2θ and glancing angle x-ray diffraction techniques. For films grown on MgO a face-centered cubic phase of TaN was observed, while films grown on SiO2 exhibited the face-centered cubic as well as a mononitride hexagonal phase. The transition temperature of the TaN deposited on SiO2 was found to be more sensitive to the nitrogen pressure during deposition as compared to the TaN deposited on MgO. [ABSTRACT FROM AUTHOR]

Abstract: A fluorine-free aqueous sol–gel technique was used to fabricate YBCO superconducting thin films. Acetic acid was added in order to modify the complexation process taking place between the metal cations and the organic chelating agents. The electrical resistance and the pH value were used as indicators of the quality of the precursors. When pH=6.5, the precursor solution had the lowest resistance, implying a good ionization of the starting metal elements. By using the optimal precursor, the film was found to have very small sized particles after pyrolysis. Consequently, the annealed YBCO films are characterized by a sharp superconducting transition with a Jc (77K) of 0.25MA/cm2. [Copyright &y& Elsevier]

We examine the vortex lattice (VL) dynamics in superconducting Nb films containing square and rectangular arrays of Ni nanodots, using ac susceptibility techniques. A remarkable robust feature is the increase in pinning that occurs for magnetic fields that create integer n or half integer flux lines per pinning cell. This phenomenology has been reported in transport experiments performed very close to the sample critical temperature TC. In our contactless experiments we determined vortex mobility and pinning properties in an extended temperature range 0.65 < T/TC < 0.99. This was possible after growing larger samples, in the square millimeters range, with top down techniques. For the square pinning array, matching up to n = 8 was observed and pinning for n = 3, 4 and 5 show different characteristics, in agreement with published simulations. For the rectangular array, some of the matching orders are missing and we do not find clear evidence of a reconfiguration transition, where vortex commensuration changes from a rectangular cell to a square cell, as reported near TC in earlier transport experiments. [ABSTRACT FROM PUBLISHER]

We present the nonlinear response of superconducting niobium nitride (NbN) thin film and NbN metamaterial with different thicknesses under intense terahertz pulses. For NbN thin film, nonlinearity emerges and superconductivity is suppressed with increasing incident terahertz electric field, and the suppression extent weakens as the film thickness increases from 15 to 50 nm. As the variation in intense terahertz fields alters the intrinsic conductivity in NbN, a consequent remarkable amplitude modulation in NbN metamaterial is observed due to the strong nonlinearity. Absorbed photo density in either NbN film or NbN metamaterial is estimated and used to understand the mechanism of nonlinear response. With a thicker NbN film element of 200 nm, the resonance of the metamaterial shows similar nonlinear modulation accompanied by a lower loss and a higher quality factor compared with a thinner NbN film element of 50 nm, which demonstrates the innovative implementation of strongly enhanced nonlinearity with thick superconducting film elements and the potential for novel applications using nonlinear metamaterial. [ABSTRACT FROM AUTHOR]