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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.

The controlled modification of superconductivity by any means, specifically in hybrid systems, has attracted much interest in the recent decades. Here, we present experimental data and phenomenological modeling on the control of TC of superconducting (SC) Nb thin films, with thickness 3 nm ≤ dNb≤50 nm, under the application of in-plane strain, S(Eex) induced by an external out-of-plane electric field, Eex to piezoelectric (PE) single crystals, namely, (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT), with x = 0.27 and 0.31. We report experimental modification of TC of Nb by Eex, accurately described by a phenomenological model that incorporates the constitutive relation S(Eex) of PMN-xPT. The systematic experimental-phenomenological modeling approach introduced here is generic and paves the way for an understanding of the underlying physical mechanisms in any SC/PE hybrid. [ABSTRACT FROM AUTHOR]

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]

A novel scheme is proposed for the study of energy transfer in a pair of coupled thin film superconducting microwave resonators. We show that the transfer could be achieved by modulating the kinetic inductance and that this has a number of advantages over earlier theoretical and experimental schemes, which use modulation of capacitance by vibrating nanobars or membranes. We show that the proposed scheme lends itself to the study of the classical analogues of Rabi and Landau-Zener-Stueckelberg oscillations and Landau-Zener transitions using experimentally achievable parameters. We consider a number of ways in which energy transfer (photon shuttle) between the two resonators could be achieved experimentally. [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]

We provide an experimental measurement of the magnetic stresses in high temperature superconducting thin films based on the Coherent Gradient Sensor which has many merits such as real time, non-destructive, full field, vibration insensitivity, etc. As an example, the radial stress, hoop stress of the YBa2Cu3O7-x (YBCO) film, and shear stress between the film and the (001) SrTiO3 substrate subjected to various magnetic fields at 40K are obtained. For the interfacial shear stress in radial direction between the film and substrate, it is found that the magnitude order of which is at GPa at somewhere under a small magnetic field. [ABSTRACT FROM AUTHOR]

The out-of-plane (c-axis) thermal conductivities of high-temperature superconducting thin films (YBa2Cu3O7-δ: YBCO) have been measured by photothermal radiometry (PTR) at room temperature. The YBCO samples are in c-axis-aligned epitaxially grown thin films with thicknesses of 250, 500, and 1000 nm. PTR is a noncontact measurement technique for the thermal conductivity and is based on the detection of infrared radiation emitted from a sample heated by a frequency-modulated laser beam. By changing the modulation frequency up to about 1 MHz, the thermal conductivity of thin film can be determined by a curve-fitting analysis of phase-lag data in the frequency domain. The uncertainty of measured thermal conductivity is estimated to be better than ±7%. The experimental results for thermal conductivity exhibit apparently positive film thickness dependence, and their absolute values are less than half of those for single crystal at the smallest thickness. The results indicate a size effect that cannot be explained by the very short phonon mean free path that the kinetic theory predicts. By employing a simple model taking into account phonon boundary scattering, the possible mean free path to interpret the present results is substantially larger than the prediction. The conclusion supports the validity of quite broad spectral distribution of phonons responsible for the thermal conductivity of YBCO. [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]

The influence of the cooling method on thermal stability is a non-trivial aspect for superconducting material to be used in several applications, for example, in photon detection. Indeed, a wasteful cooling can induce quenches in the device that can lead to false counts. So far, the efficient cooling has been realized by immersion of the superconducting device in a liquid He bath. However, cheaper cryogen-free (CF) cooling techniques are now commercially available, as well as cryocoolers are becoming the only way to obtain a cooling environment in the liquid He shortage. Here we consider three different cooling methods: one is by liquid He in a standard cryostat and the other two are a dynamic or a static He gas cooling in a CF cryostat. Then, we are able to evaluate the performance of the cooling method by the impact on current-voltage curves at very high bias currents. In particular, we acquire current-voltage characteristics on ultra-thin microbridges made by two different superconducting materials commonly used in detectors fabrication, which are NbN and NbTiN. Here, the flux-flow instability (FFI) phenomenon is used as a tool to determine the influence of the three different cooling techniques on the voltage stability of the devices under current biasing. It results that the CF cooling method has performance comparable to liquid He bath. This finding supports the spread of the CF technique for applications, and it validates the FFI as a tool to test superconducting materials. [ABSTRACT FROM AUTHOR]

Superconducting Sr1-xLaxCuO2 thin films have been grown on GdScO3 substrates by reflection high-energy electron diffraction calibrated layer-by-layer molecular-beam epitaxy. X-ray diffraction analysis has confirmed the infinite layer structure after an in situ vacuum annealing step. In situ photoemission spectroscopy indicates that the vacuum annealing step employed immediately after film growth to achieve superconducting films results in oxygen loss from the films. The superconducting critical temperature depends on the La content x, with the highest value obtained for x∼0.10. Resistivity as a function of temperature ρ(T) curves of optimally doped samples show a T2 temperature dependence characteristic of a scattering process where electron-electron interactions dominate. [ABSTRACT FROM AUTHOR]

The magneto-optical imaging technique is used to visualize the penetration of the magnetic induction in YBa2Cu3O7-δ thin films during surface resistance measurements. The in situ surface resistance measurements were performed at 7 GHz using the dielectric resonator method. When only the microwave magnetic field Hrf is applied to the superconductor, no Hrf-induced vortex penetration is observed, even at high rf power. In contrast, in the presence of a constant magnetic field superimposed on Hrf, we observe a progression of the flux front as Hrf is increased. A local thermometry method based on the measurement of the resonant frequency of the dielectric resonator placed on the YBa2Cu3O7-δ thin film shows that the Hrf-induced flux penetration is due to the increase of the film temperature. [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 Advanced Technology Centre (ATC) of National Astronomical Observatory of Japan is developing microwave kinetic inductance detectors (MKIDs) for large-array pixel cameras for millimeter and sub-millimeter astronomy. We investigated single-crystal Nb thin layers to form superconducting microresonators. We compared the performances of MKIDs based on crystalline Nb structure and those based on polycrystalline Nb. We carried out the entire manufacture of the detectors in the ATC clean room. DC magnetron sputtering is used to grow single-crystal Nb films on r-plane sapphire substrates at an elevated temperature of 800 °C. The residual resistivity ratio (RRR) measured on these single-crystal Nb layers reached values ranging from 40 to 80. We made MKIDs with this crystalline Nb layer, and we measured internal quality factors of the detectors up to 106. The measurement of the noise power spectral density of these MKIDs gave a low value of − 95 dBc/Hz from 100 Hz to 100 kHz. The internal quality factor Qi and the fractional resonance frequency change δfr/fr of MKIDs with respect to the temperature variation are usually following the extended Mattis–Bardeen equations. However, we noticed a deviation from the theoretical prediction for temperature lower than 1 K (in our case). This deviation has already been observed on Al MKIDs and explained by a theory taking into account the Kondo effect and the kinetic inductance contribution. We demonstrated that our measurements on single-crystal Nb MKIDs are also in agreement with the same theory. [ABSTRACT FROM AUTHOR]

Highlights • Superconducting MgB 2 thin film were deposited by co-deposition. • Ex-situ annealing process were done using Ar and O 2 atmospheres. • Influence of annealing atmosphere on superconducting properties were studied. • Possible mechanisms of the crystallization of MgB 2 thin film are discussed. Abstract In this work, we show that significant enhancement of superconducting properties of MgB 2 thin films prepared by vacuum evaporation and ex-situ annealing can be obtained when the annealing is performed in O 2 atmosphere instead of the usually employed inert atmosphere (Ar in the current study). Rapid annealing in O 2 significantly improves the critical transition temperature (T c), critical current density (j c), and upper critical magnetic field (H c2) compared to the control sample prepared in the same way, but annealed in Ar. Structural and composition analyses of the films demonstrate that the annealing in O 2 atmosphere produces a sufficiently thick MgO layer on the surface of MgB 2 thin films, which acts as a protective barrier preventing out-diffusion of Mg from the films during the high-temperature annealing. This consequently leads to better stoichiometry (B/Mg ratio), increased MgB 2 grain size and enhanced intergrain connectivity. The higher residual resistivity of the films annealed in O 2 atmosphere also indicates higher concentration of intragrain impurities, which causes a further increase of the j c and H c. [ABSTRACT FROM AUTHOR]

Highlights • MgB 2 films were prepared by vacuum evaporation and ex-situ annealing in O 2 and Ar. • Thick top MgO layer formed during the annealing in O 2 prevents Mg out-diffusion. • MgB 2 phase shows texture single axis [0 0 0 1] around 0–15° off the substrate normal. • During annealing also MgAl 2 O 4 and MgO are produced at the substrate-film interface. • Inner MgO layer at the MgB 2 /substrate interface is textured MgO(1 1 1)||Al 2 O 3 (0 0 0 1). Abstract Superconducting MgB 2 thin films were fabricated on c-cut sapphire substrates by vacuum co-evaporation of magnesium and boron followed by an ex situ post-annealing. We show that annealing in oxygen atmosphere can significantly improve the superconducting properties of the MgB 2 thin films compared to the typical annealing in argon atmosphere. In this work, influence of the ex-situ annealing atmosphere on the structure, texture and morphology of the superconducting MgB 2 thin films has been studied by transmission electron microscopy, X-ray diffraction and pole figure measurements. Samples annealed at 800 °C in Ar, at 800 °C in O 2 and at 500 °C in O 2 have been compared. The annealing in O 2 at 800 °C produces MgB 2 thin films with the highest superconducting transition temperature and critical current density. We show that this is thanks to the thickest MgO layer at the surface produced in this case, which acts as a protecting barrier against out-diffusion of Mg during the annealing and leads to better stoichiometry and larger MgB 2 grains compared to the samples annealed in Ar. Our method can be alternative to the customary ex-situ post annealing of Mg-B precursor in sealed vapor cell. In all samples, the MgB 2 phase showed single axis texture with the (0 0 0 1) planes slightly inclined by 0° to 15° with respect to the Al 2 O 3 (0 0 0 1) substrate surface incurred with the initial precursor evaporation geometry. During the annealing, the excess Mg also reacts with the Al 2 O 3 substrate and minor MgAl 2 O 4 and MgO phases are produced at the substrate-layer interface. [ABSTRACT FROM AUTHOR]

C-axis-aligned one-dimensional artificial pinning centers (1D-APCs) provide strong correlated pinning of magnetic vortices and enhance critical current density Jc in superconducting YBa2Cu3O7-x (YBCO) films and coated conductors. A fundamental question arises on what determines the pinning efficiency of different 1D-APCs. To shed light on this question, this work investigates the correlation between the 1D-APC/YBCO interface and the pinning efficiency of 1D-APCs of BaHfO3 (BHO) and BaZrO3 (BZO) of comparable diameters of 5–6 nm. Intriguingly, a highly coherent BHO 1D-APC/YBCO interface is revealed even at a high BHO doping level of 6 vol. %, in contrast to a semi-coherent BZO 1D-APC/YBCO interface with a large number of dislocations. This leads to a profound effect on the pinning efficiency of these 1D-APCs. Specifically, a record high pinning force density peak Fp,max ∼ 182.0 GN m−3 at Hmax > 9.0 T and 65 K is obtained in the former, which is 2.5 times of the best reported in the latter. Moreover, a ratio of Hmax to accommodation field H* determined from the 1D-APC areal concentration is found up to 3.5 in the former in contrast to 0.7 in the latter, demonstrating the critical impact of the APC/YBCO interface on the pinning efficiency of 1D-APCs. [ABSTRACT FROM AUTHOR]

Superconducting thin films with high intrinsic kinetic inductance are of great importance for photon detectors, achieving strong coupling in hybrid systems, and protected qubits. We report on the performance of titanium nitride resonators, patterned on thin films (9–110 nm) grown by atomic layer deposition, with sheet inductances of up to 234 pH/□. For films thicker than 14 nm, quality factors measured in the quantum regime range from 0.2 to 1.0 × 106 and are likely limited by dielectric two-level systems. Additionally, we show characteristic impedances up to 28 kΩ, with no significant degradation of the internal quality factor as the impedance increases. These high impedances correspond to an increased single photon coupling strength of 24 times compared to a 50 Ω resonator, transformative for hybrid quantum systems and quantum sensing. [ABSTRACT FROM AUTHOR]

Direct write patterning of high-transition temperature (high-TC) superconducting oxide thin films with a focused helium ion beam is a formidable approach for the scaling of high-TC circuit feature sizes down to the nanoscale. In this letter, we report using this technique to create a sensitive micro superconducting quantum interference device (SQUID) magnetometer with a sensing area of about 100 × 100 μm2. The device is fabricated from a single 35-nm thick YBa2Cu3O7−δ film. A flux concentrating pick-up loop is directly coupled to a 10 nm × 20 μm nano-slit SQUID. The SQUID is defined entirely by helium ion irradiation from a gas field ion source. The irradiation converts the superconductor to an insulator, and no material is milled away or etched. In this manner, a very narrow non-superconducting nano-slit is created entirely within the plane of the film. The narrow slit dimension allows for maximization of the coupling to the field concentrator. Electrical measurements reveal a large 0.35 mV modulation with a magnetic field. We measure a white noise level of 2 μΦ0/Hz1∕2. The field noise of the magnetometer is 4 pT/Hz1∕2 at 4.2 K. [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 present results for the structural, electronic, vibrational, and electron-phonon coupling properties of LaSn3 and CaSn3 adopting the simple cubic AuCu3-type structure obtained using the the generalised gradient approximation of the density functional theory and plane wave ab initio pseudopotential method. Our electronic results show that both materials display metallic character with several bands, which have mainly Sn 5p character, crossing the Fermi level. The calculated phonon spectrum of LaSn3 accords very well with reported experimental measurements. The weights of the peaks in the Eliashberg spectral function of both compounds are enhanced with the use of experimental lattice constant in our electron-phonon calculation, increasing the value of average electron phonon coupling parameter from 0.876 to 0.937 for LaSn3 (by 7%) and from 0.642 to 0.725 for CaSn3 (by 13%). The use of experimental lattice constant also improves the agreement between theoretical and experimental values of the superconducting temperature for both compounds. [ABSTRACT FROM AUTHOR]

We present results for the structural, electronic, vibrational, and electron-phonon coupling properties of LaSn3 and CaSn3 adopting the simple cubic AuCu3-type structure obtained using the the generalised gradient approximation of the density functional theory and plane wave ab initio pseudopotential method. Our electronic results show that both materials display metallic character with several bands, which have mainly Sn 5p character, crossing the Fermi level. The calculated phonon spectrum of LaSn3 accords very well with reported experimental measurements. The weights of the peaks in the Eliashberg spectral function of both compounds are enhanced with the use of experimental lattice constant in our electron-phonon calculation, increasing the value of average electron phonon coupling parameter from 0.876 to 0.937 for LaSn3 (by 7%) and from 0.642 to 0.725 for CaSn3 (by 13%). The use of experimental lattice constant also improves the agreement between theoretical and experimental values of the superconducting temperature for both compounds. [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]

Non-resonant microwave absorption (NRMA) in superconducting materials has become a new experimental technique to probe and understand superconducting materials. For example, cuprate superconductors are well studied with this technique. At the same time, the technique is also evolving. This NRMA technique has been used to study magnetic shielding effects/boundary current in Ba. K .FeAs (BaK122) single crystals of iron pnictide superconducting sample measured at 9.4 GHz below T (4.2-32 K). It has been observed that a small modulation field used in NRMA experiment yields the boundary current response. We have established that the boundary current response depends on both the modulation amplitude and the temperature. At high modulation field amplitudes and temperatures close to T , the boundary current response gets suppressed and the flux-modulated response dominates. At low temperatures far away from T , only the boundary current response dominates. [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]

The upper critical field ( B c 2 ) of superconducting thin films of Nb (film thickness d  = 40 nm) and NbN ( d   = 10, 50 and 100 nm) have been measured and analyzed as a function of temperature ( T   = 1.8–15 K) in both parallel and perpendicular magnetic field ( B   = 0–7 T) directions with respect to the film plane. Dimensional crossover from 2D to 3D is observed for all the thin films except for the 10 nm thick NbN film which exhibits only 2D behavior in the measured T and B range. Further, the upper critical fields were found to be anisotropic in case of both Nb and NbN films. However, the anisotropy shows different behavior in all the four samples. In case of Nb, below the 2D–3D crossover temperature, the B c 2 ∥ ( T ) is higher than B c 2 ⊥ ( T ) and both curves branch away further from each other. On the other hand, in case of NbN (50 and 100 nm), there is a reversal of anisotropy, i.e., in the 2D region B c 2 ∥ ( T ) > B c 2 ⊥ ( T ) and in the 3D region at some temperature B c 2 ⊥ ( T ) > B c 2 ∥ ( T ) . In the NbN films with increasing thickness, the 2D region shrinks and 3D region expands, and the 2D–3D crossover and anisotropy reversal characteristic temperatures shift toward T c . These observations are quantitatively explained using the Ginzburg–Landau theoretical approach after Schneider and Locquet (Physica C, 179 (1991) 125). [ABSTRACT FROM AUTHOR]

Heavy-ion irradiation of high-temperature superconducting thin films has long been known to generate damage tracks of amorphized material that are of close-to-ideal dimension to effectively contribute to pinning of magnetic flux lines and thereby enhance the in-field critical current. At the same time, though, the presence of these tracks reduces the superconducting volume fraction available to transport current while the irradiation process itself generates oxygen depletion and disorder in the remaining superconducting material. We have irradiated commercially available superconducting coated conductors consisting of a thick film of (Y,Dy)Ba 2 Cu 3 O 7 deposited on a buffered metal tape substrate in a continuous reel-to-reel process. Irradiation was by 185 MeV 197 Au ions. A high fluence of 3 × 10 11 ions/cm 2 was chosen to emphasize the detrimental effects. The critical current was reduced following this irradiation, but annealing at relatively low temperatures of 200 °C and 400 °C substantially restore the critical current of the irradiated material. At high fields and high temperatures there is a net benefit of critical current compared to the untreated material. [ABSTRACT FROM AUTHOR]

The high temperature superconducting YBa 2 Cu 3 O 7 − x films are widely used in various classes of microwave devices and these structures often undergo pulse magnetic field in applications. The stress behavior is of relevance to understand the mechanical response and important for assessing the safety of these superconducting structures. In this paper, we construct a theoretic model to analyze the stress behavior of a superconducting thin film-substrate system under a pulse loading (magnetic field), which is different with the well-known theoretic framework based on the Stoney formula. In the case of radial symmetry, the relationship between the stress of thin film and the electromagnetic body force is derived analytically. When a pulse loading is exerted on this film-substrate system, an analytical expression of stress dependent on the film curvature is presented, which can be considered as the foundation for the further experimental measurement. Moreover, we extend the coherent gradient sensor to kinetic measurement of the full field curvature. Using the presented model and the experimental technique, the full field stress and its evolution with time of a superconducting thin film-substrate system under a pulse magnetic field are obtained. [ABSTRACT FROM AUTHOR]

Ferromagnet/Superconductor (F/S) bilayer hybrids show exclusive states due to the mutual interaction between the superconductor and the underlying ferromagnetic substructures in micron scale. In this work, we aimed to observe the effects of the interaction between superconductivity and magnetism, especially the phenomenon involving the orientation and the size of magnetic stripes has been investigated in a coupled ferromagnetic/superconducting thin-film structure. In the proposed F/S hybrid system by this work, superconducting niobium thin-films were combined with underlying segments of ferromagnetic SmCo 5 substructures. 300 nm thick magnetic films fabricated by RF magnetron sputtering techniques were topographically grown in patterns with stripes oriented either transverse to or along the direction of current flow. The elemental and microstructural analyses were conducted by EDX, SEM and GIXRD characterization tools. Low-temperature DC transport measurements were conducted by means of four point probe method in a 9T closed-cycle cryogenic refrigeration system. Transport superconducting properties, transition temperature T C (H) and second critical field H C2 (T) were measured in a range of applied magnetic field between H = 0–9 kOe for the hybrid system. The results revealed that the artificial periodic modulation of applied field through preferentially-oriented magnetic stripes could introduce normal and superconducting channels or barriers for the current flow. [ABSTRACT FROM AUTHOR]

The HIMAC clinical study has been conducted with a carbon-ion beam since June 1994. Since 2006, as a new treatment research project, NIRS has developed both the accelerator and beam-delivery technologies for the sophisticated heavy-ion radiotherapy, which brings a pencil-beam 3D rescanning technology for both the static and moving-tumor treatments. In this technology, the depth-scanning technique was improved to the full-energy depth scanning by realizing a variable-energy operation of the HIMAC synchrotron itself. At present, a heavy-ion rotating gantry has been developed with the superconducting technology and is in a beam-commissioning stage. As a future plan, we just start a study of a multi-ions irradiation for more sophisticated LET-painting and a design study of a superconducting synchrotron for more compact heavy-ion radiotherapy facility. [ABSTRACT FROM AUTHOR]

We demonstrate an electrically tunable superconducting metamaterial capable of modulating terahertz waves dynamically. The device is based on electromagnetically induced transparency-like metamaterials, and the maximum modulation depth reaches 79.8% in the transmission window. Controlled by an electrical sinusoidal signal, such a device could achieve a modulation speed of approximately 1MHz. The superior property and simplicity of design make this device promising for the development of high performance THz systems. [ABSTRACT FROM AUTHOR]

The electrical transport properties of W films obtained through focused ion beam deposition reveal a transition from weakly insulating to metallic behavior for increasing film thickness. At low temperatures, all the films make a transition to the superconducting state. The observed stochastic distribution of the critical superconducting current is related to the occurrence of phase slip processes as documented by the statistical distribution of the depairing current and its temperature dependence according to the thermally activated model of the superconducting phase in a tilted washboard potential. [ABSTRACT FROM AUTHOR]

Superconducting thin films have been a focal point for intensive research efforts since their reduced dimension allows for a wide variety of quantum phenomena. Many of these films, fabricated in UHV chambers, are highly vulnerable to air exposure, making it difficult to measure intrinsic superconducting properties such as zero resistance and perfect diamagnetism with ex situ experimental techniques. Previously, we developed a multifunctional scanning tunneling microscope (MSTM) containing in situ four-point probe (4PP) electrical transport measurement capability in addition to the usual STM capabilities [Ge et al., Rev. Sci. Instrum. 86, 053903 (2015)]. Here we improve thisMSTMvia development of both transmission and reflection two-coil mutual inductance techniques for in situ measurement of the diamagnetic response of a superconductor. This addition does not alter the original STM and 4PP functions of the MSTM. We demonstrate the performance of the two-coil mutual inductance setup on a 10-nm-thick NbN thin film grown on a Nb-doped SrTiO3(111) substrate. [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]