We present and discuss results for the experimental evaluation of bi-SQUIDs with shunted submicron cross-type Josephson tunnel junctions characterized by low capacitance. Such a technology, meant for SQUID sensors, was developed to enable unshielded operation of the sensors and to avoid unwanted flux trapping. The obtained voltage response swing is as high as 60 µV. The observed differences between the measured and theoretically predicted voltage responses are analyzed and the possible ways to approach a triangular voltage response shape are discussed. An improved design of such bi-SQUIDs with gradiometric topology is suggested to compensate for the influence of the sizable parasitic three-junction loop, which is the main drawback of the implemented bi-SQUID topology.

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Systematic conductivity measurements in granular R _{1− x}Ce _x Ba ₂Cu ₃O _7−δ (R = Y, Er, Ho and Gd) superconductors are presented. The focus is the role of the cerium ion on the superconductor–normal transition. The results showed that the resistive transition proceeds in two stages, intragranular and intergranular, as seen by the temperature derivative of the resistivity near T _C. Therefore, from the critical exponent analysis, we have also observed two close and sharp genuine superconducting transitions in all samples investigated. Two critical temperatures were identified, but only one is strongly affected by Ce doping. The splitting of the pairing transition was associated with Ce and related to the occurrence of a phase separation. R _{1− x}Ce _x Ba ₂Cu ₃O _7−δ can be regarded as a mixed crystalline solid solution consisting of two crystal unit...

AC loss measurements in five single pancake coils wound with 4 mm wide commercial high temperature superconductor wires were carried out to investigate the dependence of coil AC loss on separation between the superconductor layers in the neighbouring coil turns ( g) and coil turn number ( N) for a given number of ampere-turns N I. The highest frequency was set at approximately 1 kHz. The AC losses measured at different frequencies agreed well with each other. AC loss in the coils with the same N increases with decreasing g. When g is increased to 1.5 times the tape width (6 mm), the loss level is similar to that in an isolated wire. Transport AC loss per unit length in the pancake coils increases with increasing turn number. However, when g is increased to 1.5 times the tape width, the loss level in the coils with different turn number is almost the same. This indicates that, at the same N I, a coil with greater

Many applications of ReBCO-coated conductors contain stacks of pancake coils. In order to reduce their high AC loss, it is necessary to understand the loss mechanisms. In this paper, we measure and simulate the AC loss and the critical current, I _c, in stacks of pancake coils (‘pancakes’). We construct stacks of up to four pancakes and we measure them by electrical means. We also obtain the anisotropic field dependence of J _c from I _c measurements of the tape. This J _c is the only input to the simulations, together with the coil dimensions. After validating our computations with the measurements, we simulate stacks of many pancakes, up to 32. We found that the AC loss in a stack of (four) pancakes is very high, two orders of magnitude larger than for a single tape. A double pancake behaves as a single one with double the width but a stack of more pancakes is very different. Finally, we found that a two-strand Roe...

We have investigated the magneto-resistivity (MR) of FeSe _{1− x}Te _x superconducting films on MgO substrate. The MR of pure FeSe and slightly Te-substituted films demonstrates regular Lorentz-type magnetic field dependence, MR ∼ B ². In highly Te-substituted samples, however, negative MR contribution due to the weak-localization effect gradually dominates at low temperature, which is consistent with the evolution of the temperature dependence of resistivity from a metallic to a weakly semiconductor-like behavior. Furthermore, the negative MR weakens and turns positive as temperature approaches the superconducting transition temperature, which is evidence for the Maki–Thompson correction in the weak-localization regime. The experimental data can be described very well by the weak-localization theory with the existence of scattering by some magnetic moments. The fitting parameters demonstrate that disorder most likely comes from the excess ...

We studied the critical state stability of a large cubic sample of single-crystalline La _1.85Sr _0.15CuO ₄ for different sample orientations with respect to the external magnetic field as well as the dynamics of the flux jumps. It is shown that thermomagnetic avalanches develop under dynamic conditions, which are characterized by the magnetic diffusivity being significantly lower than the thermal case. In this case, the critical state stability depends strongly on the cooling conditions. We compared predictions from the isothermal model and from the model for a weakly cooled sample with experimental results. In both models, the field of the first flux jump decreases with increase of the sweep rate of the external magnetic field. We also investigated the influence of the external magnetic field on the dynamics of the following stages of the thermomagnetic avalanche. It is shown that the dynamics of the flux jumps is correlated with the magnetic diffusi...

We present a new multiturn gradiometric transformer design. The transformer has a winding ratio of 1284:2 and is composed of a coplanar primary and secondary to overcome the problem of parasitic resonances typically related to planar input circuits with large winding ratios. When applied with a superconducting quantum interference device (SQUID), a highly sensitive current detector down to 25 fA Hz ^−1/2 is demonstrated. The device characterization yields a coupling coefficient of 0.39 for the transformer.

We report on our growth of superconducting SmFeAs(O, F) films by F diffusion. In our process, F-free SmFeAsO films were grown by molecular beam epitaxy (MBE) first, and subsequently F was introduced to the films via F diffusion from an overlayer of SmF ₃. We compared the growth conditions and also the properties of resultant films for CaF ₂ and LaAlO ₃ substrates. The best films on CaF ₂ exhibited a high transition temperature,  K (56.4 K) at the highest, which may exceed the highest T _c ever reported for bulk samples. Furthermore, the films on CaF ₂ also showed high critical current density over 1 MA cm ⁻² in self-field at 5 K. On the other hand, the

The possibility of the integration of a high-temperature superconductor thin film with active GaN devices at a working temperature of liquid nitrogen (77 K) are examined. We prepare YBa ₂Cu ₃O _{7− x} (YBCO) films using a pulsed-laser deposition method on a hexagonal GaN of AlGaN/GaN substrate and next create circular high electron mobility transistor (C-HEMT) structures on the same substrate. The YBCO films with a maximum critical temperature of ≈80 K were grown on an MgO buffered hexagonal GaN substrate. The YBCO films were grown at the maximum heater temperature of 760 °C. Structural properties of the YBCO films are presented. We applied a special fullerene mask and bromoethyl alcohol to avoid a YBCO film and MgO buffer layer from part of the AlGaN/GaN substrate. This was used for the preparation of the C-HEMT devices. We show that the 2DEG channel of transistors is not degraded despite applying the high-temperature deposition processes of the ...