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It is with great sadness that we report the death of Jan Evetts, who lost his second battle with cancer on 18 August 2005. In 1988 he was appointed Founding Editor of this journal where his leadership created the foundation upon which its success rests today. He made an outstanding series of contributions to the science of superconductivity and to the understanding of superconducting materials, and was an indefatigable champion of the development of applications of superconductivity. The loss to the scientific community is incalculable, as is attested by the many communications received from colleagues throughout the world.

Professor Jan Edgar Evetts (1939–2005)

Jan was born on 31 March 1939, and attended the Dragon School in Oxford, and later Haileybury. He was awarded an exhibition to read Natural Sciences at Pembroke College, Cambridge in 1958 and took his BA degree in 1961. He then undertook a Certificate of Postgraduate Study in Physics under the supervision of Professor Neville Mott. He was the first student to undertake this newly-instituted course; the title of his thesis was `The Resistance of Transition Metals'.

In 1962 he joined David Dew-Hughes' embryonic superconducting materials research group, along with Archie Campbell and Anant Narlikar. In fact it was Jan's enthusiasm for the proposed course of research that helped convince David that he should follow Professor Alan Cottrell's suggestion to apply metallurgical methodology to the study of the factors that controlled critical current density in the type II superconductors that were then under development for applications in magnets. Competing theories for the critical current density at that time were fine filaments or `Mendelssohn Sponge' versus the pinning of Abrikosov quantized vortices. The results of the group's work, to which Jan made a major contribution, came down heavily in favour of the latter theory. Jan's outstanding characteristic was his meticulous and painstaking approach to every piece of work that he tackled. His attention to detail, and his ability to design elegant experiments, was unique. He was awarded a PhD for his thesis `The Magnetisation of Superconducting Lead Alloys'. The work on flux pinning culminated in the publication of `Critical Currents in Superconductors', a research monograph (co-authored with Archie Campbell) that rapidly became the standard reference work in the field. It has recently been reprinted in the Advances in Physics `Classic Articles' series as the 9th most cited article in the journal's history (2001 Adv. Phys.50 1249–449).

Jan was appointed to a research fellowship at Pembroke College and to a Science Research Council Research Fellowship in the Department of Metallurgy in 1965. After David Dew-Hughes left Cambridge, Jan inherited the superconducting materials research group and was appointed University Demonstrator in Metallurgy and a full Fellow in Pembroke College in 1966. He progressed steadily through the various levels of academic rank, finally being appointed Professor of Device Materials in 1998. Employing an astonishing combination of administrative skill, long term planning, manipulation of the University system and high quality research at the top international level, Jan built up the largest superconductivity group in the UK, comprising some 40 members. Five of his group obtained permanent positions in the Metallurgy Department, and there are many scientists all over the world, as well as many in Cambridge, who owe their careers to him.

Jan served on many UK and European Committees, and in the organization of several international conferences. The major event of the 1980s was undoubtedly the discovery of high temperature superconductivity. Jan's group was well placed to move very rapidly into this area and the paper submitted to Nature in March 1987 was the first in the literature to report the deposition of a thin ceramic film with a 90 K superconducting transition temperature. During 1987 Jan helped co-ordinate the successful Cambridge University application to the EPSRC for an IRC in Superconductivity and he became Co-Director in charge of both the processing and the thin film and device research areas. During this very fruitful period of research a large number of basic and applied discoveries were made and some two dozen patents were filed. A novel processing method for producing textured ceramic superconductors has been successfully transferred to industry.

Jan's work on superconductivity was always paralleled by research on magnetic materials; the cross fertilization between disciplines has been very fruitful and led to him editing Pergamon's `Concise Encyclopedia of Magnetic and Superconducting Materials' in 1992. This work has been a major success with a world-wide readership.

In spite of his heavy administrative responsibilities he was always most happy when discussing the details of new research. The papers that came from his group included his name, not because he was the leader, but because in most cases the original ideas and much of the detail came from him.

In his most fundamental paper he showed how Maxwell's equations should be adapted to describe magnetic fields in superconductors. This prompted a reply from Brian Josephson, and these two papers were the first to put Maxwell's equations in superconductors on a firm basis. Jan's very elegant and physical treatment in terms of the energy of vortices was the only one to be applicable to hysteretic superconductors. Later his work became more materials-based and expanded into areas beyond superconductivity, such as magnetism. His group built up an enormous expertise in the production of thin films, which allowed them to do very elegant experiments as well as develop important practical technologies.

A topic from his graduate days, to which he would return from time to time, was that of force free configurations of flux lines and their breakdown as vortices cross each other. He was recently awarded, in collaboration with Mark Blamire, an EPSRC grant to return to this work and was looking forward to doing some fundamental research. It would be a fitting memorial if this work produces the answer to a forty-year-old problem.

He leaves a great gap and will be missed by the entire superconductivity community.

A primary difference between pure MgB₂ and its alloyed forms is that the former is a line compound and, once formed, has the same composition everywhere, whereas the latter is a solid solution and requires diffusion to move alloying elements. Since defect energies are high, this opens up the possibility that alloying elements might not be distributed homogeneously, which could have important consequences for the observed superconducting properties. To address this issue, two sets of Mg_1−xAl_xB₂ samples, with 0≤x≤0.45, were prepared from elements using reaction temperatures and times at opposite extremes of those typically reported in the literature. Sample set A was given a reaction of 1 h at 850 °C, which stopped just short of completion, while sample set B was reacted at temperatures as high as 1200 °C and thoroughly annealed for over 80 h. The trace reactants remaining after reaction A indicated that Al is taken up more slowly than Mg, thereby making compositional gradients likely. Indeed, Williamson–Hall analyses of x-ray diffraction peaks showed that set A had higher crystalline strain than set B when x>0 but not when x = 0. Since the presence of Al correlated with increased strain only for set A, it was concluded that reaction A produced substantial Al gradients across the individual grains while reaction B did not. Magnetization and heat capacity measurements indicated good bulk superconducting properties for all samples despite their structural differences, and consistent trends were observed when each sample set was considered alone. However, when both sets were considered together, their behaviour was distinct when plotted versus x (e.g. two T_c(x) curves), with trends for set A being shifted toward higher x than for set B. On the other hand, all of the data merged (e.g. one T_c(v) curve) when analysed in terms of the unit cell volume v. Thus, while the first analysis might suggest that the different reactions produced different superconducting behaviour, the second analysis, which captures the average Al content actually present inside the grains, shows that the samples have common behaviour intrinsic to the addition of Al. Moreover, these analyses show that it is important to coordinate structural and property characterizations to remove artifacts of composition gradients and uncover the intrinsic trends. Because the standard characterizations of the superconducting properties above gave no clear indication that the two sample sets had different homogeneities, the structural information was vital to make a correct assessment of the effects of Al doping on superconductivity. Since many investigations have used reactions similar to reaction A and did not analyse data in terms of structural changes, previous results should be interpreted cautiously.

Single domain Y–Ba–Cu–O (YBCO) composed of a YBa₂Cu₃O_y (Y-123) superconducting bulk matrix with discrete, non-superconducting Y₂BaCuO₅ (Y-211) phase inclusions has been fabricated by a seeded infiltration and growth (IG) technique in the form of cylindrical pellets up to 32 mm in diameter. Sample shrinkage in the radial direction for single domains prepared by this technique is relatively low at 5% and independent of sample size, in contrast to the shrinkage observed in samples grown by conventional melt processing, which increases significantly with increasing sample diameter. Furthermore, samples grown by the IG technique exhibit low porosity of typically 0.9% of the bulk volume fraction, compared with a corresponding value of around 4.9% observed in samples fabricated by conventional melt processing. Fine Y-211 particles were observed to be embedded within the Y-123 superconducting matrix for the IG processed samples, leading to a high critical current density, J_c, of over 100 000 A cm⁻² at 77.3 K in self-field. The distribution of Y-211 particles in the IG sample microstructure, however, was inhomogeneous (unlike in previous reports), which leads to a variation in the spatial distribution of J_c. The volume fraction of Y-211 in the vicinity of the seed crystal (i.e. corresponding to the initial c-sector growth stage), in particular, is typically around 5%, compared with a value of up to 30% in the a growth sectors more distant from the seed crystal (which corresponds well to the theoretical value for the sample composition studied here). The volume fraction of Y-211 inclusions in the c growth sector more distant from the seed was around 22%. Finally, a trend of the variation in the distribution of Y-211 particles in the Y-123 matrix grown by the IG technique was similar to that in sample grown by conventional melt processing.

During the last five years, the AC performance of high temperature superconductor (HTS) tapes has been under intense development due to the needs of practical applications. Previously, a system capable of measuring time dependent, spatial distribution of the magnetic flux density at a selected distance above the HTS tape has been presented. The tape can carry any cyclic current signal in the frequency range of 0–400 Hz. In this paper, a calculation model to extract information about the current densities, which create the measured magnetic flux density, is developed and used to interpret these measurements. Discrete Fourier transformation is found to provide a numerically stable method that is well suited to the interpretation of results and also for the signal noise exclusion. The third harmonic of the measured Hall voltage is seen to play an integral role in the comparison of the penetration models.

An alternative simple method is proposed for analysing the scaling properties of the high-T_c superconductor cuprates. The temperature is rescaled with a parameter T_R determined from the precise analysis of R_H(1/T), where R_H is the Hall coefficient, in the high-temperature range. To illustrate this new method, the resistivity and Hall effect data obtained on underdoped YBa₂Cu₃O_x epitaxial thin films are analysed. It is shown that the temperature-dependent resistivity ρ(T), Hall coefficient R_H(T) and the cotangent of the Hall angle cot θ_H(T) of underdoped YBa₂Cu₃O_x can be scaled into universal curves using this parameter T_R to make a linear transformation of temperature and ρ(T), R_H(T) or cotθ_H(T).

High critical current density (j_c) is one of the most important properties of high T_c superconducting thin films. Determining it is difficult especially in large films (2–3 inch). We propose a non-destructive and easy technique for measuring j_c. From measurements of the magnetic moment in the middle of a superconducting film as a function of the external magnetic field, we calculate the macroscopic critical current density.

We carried out optimal design of a Bi-2223/Ag toroidal coil for a superconducting magnetic energy storage system. The objective was to minimize the total length of Bi-2223/Ag tape at fixed conditions of operating temperature, stored energy and upper limit of the loss. The energy loss was calculated by means of the 3D finite element method (FEM) with the use of J–E expressions, which can quantitatively estimate the experimental data obtained from the tape in wide ranges of temperature (20–77 K), external magnetic field (0.02–3 T) and its applied direction (arbitrary). On the other hand, the optimal solution was obtained by a genetic algorithm (GA), which was a particularly effective optimization method when the objective function had a number of local minimum points. We performed such optimal design under various constraint conditions, and found that the optimal configuration of the coil drastically changed as its operating temperature varied.

The effects of Gd addition on the phase evolution and superconducting properties of (Bi, Pb)-2212 prepared in the bulk polycrystalline form were studied. The Gd content in the samples was varied from 0.0 to 0.5 on a general stoichiometry of Bi_1.7Pb_0.4Sr_2.0Ca_1.1Cu_2.1Gd_xO_y. Phase analysis by means of x-ray diffraction, microstructural examination by scanning electron microscopy and superconducting property studies were carried out to evaluate the relative performances of the samples. It is observed that Gd addition enhances the transition temperature (T_C) and critical current density (J_C) of the system. Moreover no secondary phase containing Gd ions or any other cations was observed after the final stage of heat treatment. Microstructural examination shows clear and distinct morphologies for the Gd-added samples, wherein the grain growth is suppressed by the addition of Gd and the edges of the grains become more and more rounded. As a result, there is an increase in the porosity of the Gd-added samples, leading to a reduction in the sintered density for these samples.

Critical current densities J_c of MgB₂ thin films have been measured; these were prepared by an electron beam evaporation method without any post-annealing. In order to improve the characteristics of J_c in high magnetic fields, a MgB₂ thin film was deposited in an O₂ atmosphere. The values of J_c of the O₂-doped film have exceeded those of the non-doped film in magnetic fields applied perpendicular and also parallel to the c-axis. The peak of J_c caused by the c-axis correlated pinning centres has been observed in the angular dependence of J_c. The upper critical field B_c2 and the vortex glass–liquid transition field B_g have been estimated from temperature dependences of resistivity curves in both directions of the magnetic fields perpendicular and parallel to the c-axis. It is found that B_c2 and B_g are increased by the introduction of O₂ in both the directions of the applied field. This fact indicates that effective pinning centres have been introduced by the deposition of the MgB₂ thin film in an O₂ atmosphere.

We analysed some of the structural properties of BI₂Sr₂CaCu₂O_8+x superconductors using neutron scattering and intelligent gravimetric analyser instruments from room temperature to 750 °C. Both of the experiments showed that the oxygen content of the compound is temperature dependent and decreases as the temperature increases. Neutron experiment results showed that the lattice parameters of the compound are a function of oxygen content and they increase as the oxygen content decreases.

Low-cost and commercially viable processes to fabricate coated conductors are necessary for application in electric-power technologies. We demonstrate the chemical solution growth of CeO₂ buffer and YBCO layers on IBAD-YSZ/Hastelloy templates. Very good biaxially textured CeO₂ buffer layers can be formed by the chemical solution method using inorganic cerium nitrate precursors. Through control of the solution molarity, very uniform, smooth, and dense CeO₂ buffer layers can be obtained. Subsequently, the YBCO films were deposited by metallorganic deposition using the trifluoroacetic (TFA-MOD) method. High-critical-current-density (J_c) YBCO films were obtained, with the transport current density of about 1.2 MA cm⁻² (77 K, 0 T). The onset transition temperature is as high as 94.5 K, and the transition width is about 1.3 K. Hence, the mature IBAD technique, combined with the low-cost solution method, can provide a very promising robust process for fabrication of low-cost YBCO coated conductor on a large scale.

The influence of the nature of the boron precursor on the superconducting properties of polycrystalline MgB₂ was studied. Critical current densities (J_c) for MgB₂ made from high purity amorphous boron are at least a factor of three higher than typical values measured for standard MgB₂ samples made from amorphous precursors. Two possible mechanisms are proposed to account for this difference.

Samples made from crystalline boron powders have around an order of magnitude lower J_c compared to those made from amorphous precursors. X-ray, T_c and resistivity studies indicate that this is as a result of reduced current cross-section due to the formation of (Mg)B–O phases. The samples made from amorphous B contain far fewer Mg(B)–O phases than crystalline B despite the fact that the amorphous B contains more B₂O₃. The different reactivity rates of the precursor powders accounts for this anomaly.

A comprehensive study of the correlation between various structural (Δω°, c-axis), electrical (T_c, ΔT) and linear microwave properties (R_s(T₀), λ(T₀) and σ₁(T₀)) of epitaxial YBCO thin films on MgO and LaAlO₃ substrates, and also their nonlinear microwave properties (H_rf^*, d R_s/d H_rf, H_{rf _ TOI}², m-slope and H_{rf _ 30 dB}²) has been performed. It was found that among the numerous parameters from the first group, the nonlinear microwave properties appear to correlate well only with the low-temperature penetration depth λ(T₀), residual quasiparticle conductivity σ₁(T₀) and the c-axis lattice parameter. Here, among those three parameters the best correlation of the nonlinear properties is observed with λ(T₀). The correlation of the other parameters from the first group with the nonlinear microwave performance of the films is either not evident, because of the wide spread of the data, or absent. There is also seen a correlation within the group of linear microwave parameters (such as R_s(T₀), σ₁(T₀) and λ(T₀)) and partial correlation within the group of the nonlinear parameters (such as H_rf^*, d R_s/d H_rf and H_{rf _ TOI}²). However, all the aforementioned correlations seem to be dependent on many conditions (such as film growth technique and substrate), and are by no means quantitative, but only qualitative.

The paper reports on a new design of the magnetoscan technique. Due to a modification in the original magnetoscan design, a significant improvement in resolution was obtained. The paper focuses on experimental results which should support the idea of the new design using two magnets with opposite direction of magnetization. This contribution to the characterization techniques of melt-grown bulk superconductors should promote the easy installation of this technique in industry. The improved magnetoscan technique may further help to investigate growth-induced inhomogeneities of the top-seeded-melt-growth (TSMG) process in the submillimetre range, and it offers new possibilities for the characterization of smaller structures such as superconducting films or coated conductors.

Hot spots are one of the main limitations in the development of large-scale high-power applications with superconducting materials. The application of digital speckle interferometry to detect inhomogeneous heating on ceramic superconductors allows the determining of a hot spot location in these materials before any damage is caused to the material. The technique detects deformations that are induced in the material due to dilatation, attaining a resolution of 0.45 µm /fringe. In this paper this technique has been applied to analyse the heating generation in Bi-2212 superconducting monoliths at room temperature and in operation conditions. In the first case a homogeneous heating is obtained, leading to a parallel fringe pattern. In the second case, a situation with an inhomogeneous heating origin has been detected. Once the position of this hot spot is determined, microstructure studies have been performed to determine which defects are responsible for hot spot generation.

A promising approach used to fabricate YBa₂Cu₃O_7−δ (YBCO) thin films is the metal–organic deposition (MOD) method using trifluoroacetate (TFA) solution. In this method, the heating rate is known to be a crucial parameter and an important variable for optimization. However, there does not seem to be an in-depth understanding of the materials issues associated with different heating rates. Some aspects of this correlation have been addressed in this paper, where the influence of the heating rate during calcination in the 200–250 °C temperature range on the surface chemistry, morphology, and electrical properties has been studied. X-ray photoelectron spectroscopy reveals similar chemical compositions and almost complete decomposition of metal trifluoroacetates at all heating rates. However, the heating rate is seen to have a significant influence on the morphology of the calcined film, and leads to great changes in the final film. When a TFA film is heated through the 200–250 °C step at 3 °C h⁻¹, it has a smooth and uniform surface. On the other hand, a slower heating rate (1.5 °C h⁻¹) results in phase separation during calcination, and a faster heating rate (10 °C h⁻¹) leads to a rough film decorated with micron-scale pores. This leads to the final reacted films having very different microstructures. A uniform, c-axis oriented microstructure is observed in the 3 °C h⁻¹ heated films. A slower heating rate results in a large density of a-axis oriented grains and a faster heating rate causes higher pore density together with a bigger average pore size. Although all films exhibit high phase purity YBCO with noticeable c-axis orientation, the electrical resistivity (ρ) for the normal state (100 K) shows an increasing sequence of ρ(3 °C h⁻¹)< ρ(10 °C h⁻¹) <ρ(1.5 °C h⁻¹). In this experiment set-up, the highest J_c value of 1.3 × 10⁶ A cm⁻² (77 K, self-field) was achieved with a 3 °C h⁻¹ heating rate, which can be correlated with texture and microstructural observations.

Nanodot arrays of Y₂O₃ were dispersed in thin films of YBa₂Cu₃O_7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density J_c both in applied magnetic field and self-field is enhanced by as much as an order of magnitude, along with a significant increase in the irreversibility field H_irr. High-resolution scanning transmission electron microscopy (STEM) and Z-contrast STEM show that the nanoparticles are crystalline and coherent with the YBCO matrix. Whereas in most other studies pinning has been attributed to the strain fields around the nanoparticles, in this case pinning may actually be due to the nanoparticles themselves, since the delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles.

We predict that below T_c a regime of negative differential conductivity (NDC) can be reached. The superconductor should be supercooled to T<T_c in the normal phase under DC voltage. In such a nonequilibrium situation the NDC of the superconductor is created by the excess conductivity of the fluctuation Cooper pairs. We propose NDC of supercooled superconductors to be used as an active medium for generation of electric oscillations. Such generators can be used in the superconducting electronics as a new type THz source of radiation. Oscillations can be modulated by the change of the bias voltage, electrostatic doping by a gate electrode when the superconductor is the channel of a field effect transistor, or by light. When small amplitude oscillations are stabilized near the critical temperature T_c the generator can be used as a bolometer. NDC, which is essential for the applications, is predicted on the basis of analysis of known results for fluctuation conductivity, obtained in previous papers by solving the Boltzmann kinetic equation for the Cooper pairs metastable in the normal phase. The Boltzmann equation for fluctuation Cooper pairs is a result of state-of-the-art application of the microscopic theory of superconductivity. Our theoretical conclusions are based on some approximations like time dependent Ginzburg–Landau theory initially derived for gapless superconductors, but nevertheless can reliably predict the appearance of NDC. NDC is the main ingredient of the proposed technical applications. The maximal frequency at which superconductors can operate as generators is determined by the critical temperature . For high-T_c superconductors this maximal frequency falls well inside the terahertz range. Technical conditions to avoid nucleation of the superconducting phase are briefly discussed. We suggest that nanostructured high-T_c superconductors patterned in a single chip can give the best technical performance of the proposed oscillator.

Hexagonal plate-shaped MgB₂ crystals have been prepared at ambient pressure. A superconducting transition has been observed at 37 K with a large transition width of ΔT_c∼22 K. The lattice strain (0.7%) is calculated from the FWHM of XRD data. Both an edge dislocation with Burgers vector b = −a, and a Mg (nano-agglomerate) self-ordering superstructure with lattice constant 2a₀ have been directly detected in the [001] direction by HRTEM. The very broad transition may be caused by these defects in the crystals.

We discuss oscillation and radiation of a superconducting ring in a nonuniform magnetic field produced by a Helmholtz coil. This is a simple example of the oscillation of a superconductor between two magnets. Two oscillation modes (the parallel mode and the antiparallel mode) exist, depending on the directions in which the currents flow in the two coils of the Helmholtz coil. Calculations show the following facts. (i) A characteristic radius-to-height ratio of the Helmholtz coil where a maximum frequency can be produced exists. (ii) As the temperature increases, both the parallel and the antiparallel mode frequencies are fixed, but the parallel mode frequency starts to decrease and falls to 0 in a temperature region below the critical temperature, indicating an oscillation in the intermediate state. (iii) When the superconducting ring oscillates with trapped flux in it, as the trapped flux increases, the parallel mode frequency decreases, but the antiparallel mode frequency increases. When the frictional force is not present, radiation alone reduces the motion energy. We show that the oscillations in both modes stop as time approaches infinity. Over time, the amplitude decreases in the form of a root inverse for the parallel mode and decreases exponentially for the antiparallel mode. The half-lives of the amplitudes have been calculated as 2.1 × 10²³ years for the parallel mode and 6.9 × 10²³ years for the antiparallel mode.

For a few years there has been an increasing effort to study the impact of (bending) strain on the transport properties of superconducting wires. As the stress distribution, originated by differences in the thermal expansion and electromagnetic load, is the driving factor for the final strains, the axial and transverse stiffness of the strand play a crucial role in the final performance. Since the strain state of the Nb₃Sn filaments in strands determines the transport properties, basic experimental stress–strain data are required at the strand level for accurate modelling and analysis and eventually for optimizing cable and magnet design. We performed axial tensile stress–strain measurements on several types of Nb₃Sn strands used for the manufacture of the International Experimental Thermonuclear Reactor (ITER) central solenoid and toroidal field model coils and a powder-in-tube processed wire. In total 48 wire samples were tested at boiling helium, boiling nitrogen and at room temperature. We present the computation of the stress–strain characteristic with a straightforward 1D model using an independent materials database, obtaining a good agreement with the experimental results.

The details from the take-off origin of the measured stress–strain curves are discussed and the data are evaluated with respect to some commonly used functions for fitting stress–strain curves. The measurements are performed in the new setup TARSIS (test arrangement for strain influence on strands). A double extensometer connected to the sample enables us to determine the strain level whereas a load cell is used to monitor the stress level.

For higher levels of applied stress (100 MPa), we found typically a higher strain for bronze route wires compared to a powder-in-tube and internal tin type of strand. Stress–strain results are essential to assess more accurately the impact of thermal and electromagnetic induced stress on the strain state of the Nb₃Sn filaments for wires from various manufacturing processes.

The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa₂Cu₃O_7−δ (YBCO), in the form of self-assembled stacks of BaZrO₃ (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ∼2–3 nm and an areal density ('matching field') of 8–10 T for 2 vol.% incorporation of BaZrO₃. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, J_c, varies as J_c∼H^−α, with α∼0.3 rather than the usual values 0.5–0.65. Similar results were also obtained for CaZrO₃ (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

A description of a field-cooling superconducting phase transition in large-scale one-dimensional π-loop arrays is given by analysing the free energy of the arrays with a simplified model. The analysis shows that the transition of the arrays splits into two phase branches, the magnetizations with either ferromagnetic or anti-ferromagnetic ordering, which depend periodically on the strength of external magnetic flux ϕ_e through each loop and monotonically on the screen parameter β of the loops in the arrays. The influence of the thermal fluctuation effect on the ordering during the transition from normal to superconducting states of the π-loop arrays is briefly discussed.