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The phenomenon of Berezinskii–Kosterlitz–Thouless (BKT) phase fluctuations and the superconducting fluctuations is investigated in a 40 nm thick granular aluminum film using magneto-transport measurements. The transport measurements suggest the possibility of strong electron–phonon (el–ph) interactions in contrast to a Bardeen–Cooper–Schrieffer superconductor. It shows a BKT transition of 2.304 K and a superconducting mean-field transition at 2.32 K. The presence of the resistive tail even before the BKT transition reflects the abundance of thermally activated free vortices. By analyzing the excess conductivity, Gaussian–Ginzburg–Landau superconducting fluctuations are observed above the superconducting transition, which causes rounding of the transition region even before the superconducting transition. The temperature dependence of the fluctuation conductivity in zero magnetic field exhibits distinct signatures of the two-dimensional direct Aslamazov–Larkin theory, with a significant contribution from the Maki–Thompson (MT) model. Furthermore, the anomalous behavior of the fluctuation conductivity at higher temperatures and perpendicular magnetic fields (up to 700 mT) is explained in terms of the total-energy cutoff (=0.72) in the low-wavelength region of the superconducting fluctuations and a pair-breaking parameter (∼0.031). Further studies on the pair-breaking parameter indicate the presence of the el–ph scattering, which diminishes the MT contribution. Our study carries important bearings on how the BKT phase fluctuations and superconducting amplitude fluctuations control the conductivity of granular superconductor near and above the transition region as non-equilibrium properties of weakly disordered granular superconductors. This research is of significance, offering insights into the fundamental properties of granular superconductivity and aiding in the comprehension of nano-structured thin film devices. [ABSTRACT FROM AUTHOR]

This study presents an approach to achieve a triaxial magnetic alignment through a linear drive type of modulated rotating magnetic field by using a permanent magnet array. This magnet array generates a modulated rotating magnetic field (MRF) without moving the sample and can produce an MRF of ∼ 0.8 T. By utilizing this magnet array, DyBa2Cu3Oy (Dy123, y ∼ 7) grains were biaxially aligned. After cutting the as-aligned sample that was magnetically aligned, we observed a location dependence of the orientation degree. We achieved the higher in-plane orientation degree of ∼ 8.5° and the c-axis orientation degree of ∼ 6.0°, respectively. The 3D simulation analysis played a key role in identifying the region where the uniformity of the MRF is within the magnet array. Compared to the epitaxial growth techniques, the use of the magnet array offers a cost-effective and versatile solution for achieving triaxial magnetic alignment. [ABSTRACT FROM AUTHOR]

We present a MgB2-based Microwave Kinetic Inductance Detector (MKID) featuring a quality factor Qi ~ 105 and noise equivalent power NEP ~ 10−14  W / Hz at 2 K. In comparison to YBCO-based MKIDs, the MgB2 detector shows greater sensitivity to both temperature and magnetic field, a result of its two-gap nature and relatively low critical H c 2 field. Our data indicate that MgB2 is more advantageous for MKID applications at temperatures lower than 3 K. [ABSTRACT FROM AUTHOR]

The emergence of Majorana fermion bound states has been studied in several environments. In this paper, we discuss the current-voltage characteristics of a Majorana fermion state as a function of the voltage, temperature, and magnetic field and compare the results to experiment. Based on the agreement and identified parameters, we calculate the noise as possible proof of the emergence of Majorana fermions. [ABSTRACT FROM AUTHOR]

The superconducting quantum interference (SQI) patterns of Josephson junctions fabricated from hybrid structures that interface an s-wave superconductor with a topological insulator can be used to detect signatures of novel quasiparticle states. Here, we compare calculated and experimental SQI patterns obtained from hybrid junctions fabricated on cadmium arsenide, a two-dimensional topological insulator. The calculations account for the effects of Abrikosov (anti-) vortices in the superconducting contacts. They describe the experimentally observed deviations of the SQI from an ideal Fraunhofer pattern, including anomalous phase shifts, node lifting, even/odd modulations of the lobes, irregular lobe spacing, and an asymmetry in the positive/negative magnetic field. We also show that under a current bias, these vortices enter the electrodes even if there is no intentionally applied external magnetic field. The results show that Abrikosov vortices in the electrodes of the junctions can explain many of the observed anomalies in the SQI patterns of topological insulator Josephson junctions. [ABSTRACT FROM AUTHOR]

Thermal switching by magnetic fields is one of the important functionalities in thermal management technologies. In low-temperature devices, superconducting states can be used as a magneto-thermal-switching (MTS) component because carrier thermal conductivity (κ) is strongly suppressed in superconducting states. Recently, we demonstrated that the MTS ratio (MTSR) of pure Nb reached 650% at a temperature (T) of 2.5 K under a magnetic field (H) of 4.0 kOe [Yoshida et al., Appl. Phys. Express 16, 033002 (2023)]. In this study, to enrich knowledge on MTS of superconductors, the MTSRs of pure Pb wires with 5 N and 3 N purities were investigated by measuring the temperature or magnetic-field dependences of κ. For 5N-Pb, a large MTSR exceeding 1000% was observed below 3.6 K under H > 600 Oe. Although higher MTSRs were expected at lower temperatures under H > 600 Oe, the obtained data under those conditions were accompanied by large errors due to magnetic-field-induced huge κ at low temperatures. In contrast, the κ for 3N-Pb was observed to be clearly lower than that for 5N-Pb. Although the magnetic-field-induced change in κ was small, the MTSR at T = 2.5 K was 300%. These results suggest that Pb is a promising material for low-temperature magneto-thermal switching because of wide-range κ tunable by magnetic field and purity. [ABSTRACT FROM AUTHOR]

A simplified model of anisotropic magnetic susceptibility in the Meissner–London vortex-free state of cuboidal superconducting samples is presented. Using this model, precision measurements of the magnetic response in three perpendicular directions of a magnetic field with respect to primary crystal axes can be used to extract the components of the London penetration depth, thus enabling the evaluation of the general superfluid density tensor, which is needed in the analysis of the superconducting gap structure. [ABSTRACT FROM AUTHOR]

Nonreciprocal transport effects can occur in the normal state of conductors and in superconductors when both inversion and time-reversal symmetry are broken. Here, we consider systems where magnetochiral anisotropy of the energy spectrum due to an externally applied magnetic field results in a rectification effect in the normal state and a superconducting (SC) diode effect when the system is proximitized by a superconductor. Focusing on nanowire systems, we obtain analytic expressions for both normal state rectification and SC diode effects that reveal the commonalities—as well as differences—between these two phenomena. Furthermore, we consider the nanowire brought into an (almost) helical state in the normal phase or a topological SC phase when proximitized. In both cases, this reveals that the topology of the system considerably modifies its nonreciprocal transport properties. Our results provide insights into how to determine the origin of nonreciprocal effects and further evince the strong connection of nonreciprocal transport with the topological properties of a system. [ABSTRACT FROM AUTHOR]

We report on a novel TaNbZrHfTi-based high entropy alloy (HEA) which demonstrates distinctive dual-phase superconductivity. The HEA was synthesized under high pressures and high temperatures starting from a ball milled mixture of elemental metals in a large-volume Paris–Edinburgh cell with P ≈ 6 GPa and T = 2300 K. The synthesized HEA is a phase mixture of BCC (NbTa)0.45(ZrHfTi)0.55 with Tc1 = 6 K and FCC (NbTa)0.04(ZrHfTi)0.96 with Tc2 = 3.75 K. The measured magnetic field parameters for the HEA are lower critical field, Hc1(0) = 31 mT, and a relatively high upper critical field, Hc2(0) = 4.92 T. This dual-phase system is further characterized by the presence of a second magnetization peak, or the fishtail effect, observed in the virgin magnetization curves. This phenomenon, which does not distort the field-dependent magnetization hysteresis loops, suggests intricate pinning mechanisms that could be potentially tuned for optimized performance. The manifestation of these unique features in HEA superconductivity reinforces phase-dependent superconductivity and opens new avenues in the exploration of novel superconducting materials. [ABSTRACT FROM AUTHOR]

Superconducting junctions with a ferromagnet as the weak link, where triplet correlations can transport supercurrents over a substantial distance, have been of long-standing interest. In this work, we study the triplet transport in planar La0.7Sr0.3MnO3 (LSMO) nanowire Josephson junctions with NbTi superconducting contacts. By meticulous ion etching with an artificial Pt hard mask, the NbTi/LSMO bilayer is structured to form an LSMO bridge without damaging its top layer. We observe superconducting (critical) currents of the order of 109 A/m2 in a junction with a length of 1.3 μm, and distinguishing superconducting quantum interference (SQI) patterns when sweeping a magnetic field perpendicular ( B ⊥ ) to the plane of the wire or parallel ( B ∥ ) to the plane and along the wire. The observed Gaussian-shaped SQI pattern is attributed to the diffusive transport of triplet pairs in the LSMO. Our work demonstrates that combinations of oxide magnets with conventional (s-wave) alloy superconductors can be a promising new route to realizing superconducting spintronics. [ABSTRACT FROM AUTHOR]

The standard superconducting oxides technique for synthesising superconducting oxides was applied under normal pressure to prepare the Tl2Ba2Ca2Cu3O10-δ (Tl-2223) superconductor. It is found the optimal conditions and synthesis methods to achieve the formation and stability of the high phase Tl-2223, as well as the appropriate working ranges for the samples to obtain the best superconductor characteristics. The X-ray diffraction (XRD) analysis demonstrated the formation of the tetragonal phase of Tl-2223. The transition behaviour of sample was studied using high magnetic fields ranging from zero T to 10T. The results demonstrated an estimated critical magnetic field (Hc2) of about 20T and a long coherence length of approximately 4 nm. The transition temperature of about 122 K and the direct current (DC) susceptibility of the superconductor were calculated. It was noted that with an increase in the applied magnetic field, both the transformation temperature and the DC susceptibility values decreased at T = 0 K. These findings provide important insights into the properties and behaviour of Tl-2223 under different conditions. [ABSTRACT FROM AUTHOR]

This study examined the impact of adding hard ferrite Ba0.5Sr0.5Fe12O19 (BSF) nanoparticles to the Bi1.8Pb0.4Sr2Ca2Cu3.2O10+δ (Bi, Pb)-2223) superconductor phase. The investigation specifically focused on evaluating the critical current density, fluctuation-induced conductivity, and magnetoresistance of nano-(BSF)x/(Bi, Pb)-2223 composite, where 0.00 ≤ x ≤ 0.20 wt.%. The results revealed that the critical current density, Jc, increased with the addition of nano-(BSF) up to x = 0.04 wt.%, reaching a value of 441.20 A/cm2. The Aslamazov and Larkin (A–L) approach has been evaluated the fluctuation-induced conductivity. Several superconducting parameters, including coherence length ζc(0), effective layer thickness d, penetration depth λpd(0), and Fermi energy E F showed improvement as the concentration of nano-(BSF) increased up to x = 0.04 wt.%. In addition to Ginzburg–Landau critical parameters, such as the thermodynamic critical field Bc(0), lower critical magnetic field Bc1(0), upper critical magnetic field Bc2(0), and critical current density Jc(0) demonstrated an increase up to x = 0.04 wt.%, followed by a decrease for higher concentrations. The magnetoresistance measurements were performed at various applied DC magnetic fields, with values ranging from 0.29 to 4.44 kG, and were analyzed using the thermally activated flux creep (TAFC) and Ambegaokar–Halperin (AH) models. The calculated flux pinning energy (U) increased with the addition of nano-(BSF) up to x = 0.04 wt.% and then decreased for x > 0.04 wt.%. Furthermore, the transition width (ΔT), was observed to increase as the applied magnetic field values increased. Moreover, the addition of nano-(BSF) increased the field-independent critical current density, Jc,0(0), up to x = 0.04 wt.%, after which it decreased for higher concentrations. [ABSTRACT FROM AUTHOR]

Here, we demonstrate superconducting Dayem-bridge weak-links made of different stoichiometric compositions of NbRe. Our devices possess a relatively high critical temperature, normal-state resistance, and kinetic inductance. In particular, the high kinetic inductance makes this material a good alternative to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the realization of superinductors and high-quality factor resonators, whereas the high normal-state resistance yields a large output voltage in superconducting switches and logic elements realized upon this compound. Moreover, out-of-plane critical magnetic fields exceeding 2 T ensure that possible applications requiring high magnetic fields can also be envisaged. Altogether, these features make this material appealing for a number of applications in the framework of quantum technologies. [ABSTRACT FROM AUTHOR]

As a highly regarded superconducting material with a concise layered structure, MgB2 has attracted significant scientific attention and holds vast potential for applications. However, its limited current-carrying capacity under high magnetic fields has greatly hindered its practical use. To address this issue, we have enhanced the superconducting performance of MgB2 by incorporating inhomogeneous phase nanostructures of p-n junctions with electroluminescent properties. Through temperature-dependent measurements of magnetization, electronic specific heat, and Hall coefficient under various magnetic fields, we have confirmed the crucial role of inhomogeneous phase electroluminescent nanostructures in improving the properties of MgB2. Experimental results demonstrate that the introduction of electroluminescent inhomogeneous phases effectively enhances the superconducting performance of MgB2. Moreover, by controlling the size of the electroluminescent inhomogeneous phases and optimizing grain connectivity, density, and microstructural uniformity, we can further improve the critical temperature (TC) and flux-pinning capability of MgB2 superconducting materials. Comprehensive studies on the physical properties of MgB2 superconducting structures added with p-n junction electroluminescent inhomogeneous phases also confirm the general effectiveness of electroluminescent inhomogeneous phases in enhancing the performance of superconducting materials. [ABSTRACT FROM AUTHOR]

Struts of a superconducting YBa2Cu3Oy (YBCO) foam prepared by the infiltration growth method on the base of commercial polyurethane foams were extracted from the bulk, and thoroughly characterized concerning the microstructure and the magnetoresistance, measured by the four-point technique. Optical microscopy, electron microscopy, electron backscatter diffraction and atomic force microscopy observations indicate a unique microstructure of the foam struts which shows a large amount of tiny Y2BaCuO5 (Y-211) particles (with diameters between 50 and 100 nm) being enclosed in channel-like grain boundaries between the YBCO grains and a one-of-a-kind surface of the struts covered with Ba3Cu5Oy-particles. The resistance data obtained at temperatures in the range 4.2 K ≤ T ≤ 150 K (applied magnetic fields ranging from 0 to 7 T) were analyzed in the framework of the fluctuation-induced conductivity (FIC) approach using the models of Aslamazov–Larkin (AL) and Lawrence–Doniach (LD). The resulting FIC curves reveal the presence of five distinct fluctuation regimes, namely, the short-wave (SWF), one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and critical (CR) fluctuation domains. The analysis of the FIC data enable the coherence length in the direction of the c-axis at zero-temperature ( ξ c (0) ), the irreversibility field ( B irr ), the upper critical magnetic field ( B c 2 ), the critical current density at T = 0 K ( J c (0) ) and several other parameters describing the the material's superconducting properties to be determined. The present data reveal that the minuscule Y-211 particles found along the YBCO grain boundaries alter the excess conductivity and the fluctuation behavior as compared to conventional YBCO samples, leading to a quite high value for J c (0) for a sample with a non-optimized pinning landscape. [ABSTRACT FROM AUTHOR]

In this work we studied the vortex-configuration in a mesoscopic superconducting square in presence of an external magnetic field H applied parallel to its surface vector. We study the magnetization curves in a complete loop, the magnretic induction and the superconducting-electron density for the sample considering Neumann boundary conditions for the order parameter, via length Gennes extrapolation (b → ∞). The sample presents a pinnin center as a Kagome-type laticce at different critical temperature. We solve the generalized time-dependent Ginzburg-Landau equations for a two-condensate system using the Link-variable method considering a Field-Cooling process. Our results show that the vortices are always located at the pinning centers in non-conventional configurations, due to cuopling used. [ABSTRACT FROM AUTHOR]

In planar superconductor thin films, the places of nucleation and arrangements of moving vortices are determined by structural defects. However, various applications of superconductors require reconfigurable steering of fluxons, which is hard to realize with geometrically predefined vortex pinning landscapes. Here, on the basis of the time-dependent Ginzburg–Landau equation, we present an approach for the steering of vortex chains and vortex jets in superconductor nanotubes containing a slit. The idea is based on the tilting of the magnetic field B at an angle α in the plane perpendicular to the axis of a nanotube carrying an azimuthal transport current. Namely, while at α = 0 ∘ , vortices move paraxially in opposite directions within each half-tube; an increase in α displaces the areas with the close-to-maximum normal component | B n | to the close(opposite)-to-slit regions, giving rise to descending (ascending) branches in the induced-voltage frequency spectrum f U (α) . At lower B values, upon reaching the critical angle α c , the close-to-slit vortex chains disappear, yielding f U of the n f 1 type ( n ≥ 1 : an integer; f 1 : the vortex nucleation frequency). At higher B values, f U is largely blurry because of multifurcations of vortex trajectories, leading to the coexistence of a vortex jet with two vortex chains at α = 90 ∘ . In addition to prospects for the tuning of GHz-frequency spectra and the steering of vortices as information bits, our findings lay the foundation for on-demand tuning of vortex arrangements in 3D superconductor membranes in tilted magnetic fields. [ABSTRACT FROM AUTHOR]

We investigate the influence of the Abrikosov vortex lattice on the Casimir force in a setup constituted by high-temperature superconductors subject to an external magnetic field. The Abrikosov lattice is a property of type II superconductors in which normal and superconducting carriers coexist and the latter define a periodic pattern with square symmetry. We find that the optical properties determined by spatial redistribution of the superconducting order parameter induce Casimir forces with a periodic structure whose minimal strengths coincide with the vortex cores. [ABSTRACT FROM AUTHOR]

We have investigated the superconducting properties of nanocomposite pellets made from Bi-2223 and Co2C powders. Our measurements reveal loss of superconducting fraction in the nanocomposites. However, the retained superconducting fraction exhibits robust bulk superconducting properties. The Tc of the retained superconducting fraction was 109 K, which was found to be comparable to that of the pure Bi-2223 pellet. We found that the composite's net magnetization response is a superposition of the contributions of ferromagnetic and superconducting fractions. Analysis revealed that the surviving superconducting fraction exhibits a robust Meissner response. In the nanocomposite, the irreversibility field of the superconducting fraction at 77 K is found to increase by almost three times compared to the pristine material, thereby showing strong vortex pinning features. We also find a broadened magnetic field regime over which we observe that a single vortex pinning regime sustained in the nanocomposite. The critical current density, Jc, of the nanocomposite was found to be approximately five times higher than that of the pristine Bi-2223 pellet at low T. In fact, the enhancement in Jc is most significant in the high T regime, where at temperatures close to Tc in the nanocomposite, we see almost two orders of magnitude increase in Jc compared to the pristine Bi-2223 pellet. Our study suggests that larger sized agglomeration of magnetic nanoparticles of Co2C leads to loss of superconductivity in the nanocomposite. However, there are also unagglomerated Co2C nanoparticles distributed uniformly throughout the nanocomposite, which act as efficient pinning centers that allow for collective vortex pinning centers to be retained, even up to temperatures near Tc, and these nanoparticles also do not compromise the bulk Tc of the superconducting fraction. Our study shows that these nanocomposites that exhibit enhanced Jc especially in the high T regime are potentially useful for high current applications. [ABSTRACT FROM AUTHOR]

We have developed Nb-rod method Cu-Nb reinforced Nb3Sn wires (Cu-Nb/Nb3Sn wires), which have significantly improved superconducting characteristics under mechanical stress compared to conventional Nb3Sn wires. Cu-Nb/Nb3Sn wires can be manufactured into coils not only with the conventional wind-and-react (W&R) method but also with the react-and-wind (R&W) method, and the superconducting performance and the mechanical characteristics are both improved by a strain control through pre-bending treatment. Furthermore, elemental technology developments for a higher strength, a higher critical current density, a rectangularization, an enamel coating, a thinner wire for small radius bending, and a stranded wire have made them practical wires with an excellent manufacturability. In the future, Cu-Nb/Nb3Sn wires will be expected to be applied in advanced superconducting equipment such as a high magnetic field NMR/MRI, a particle accelerator, and a large fusion reactor. [ABSTRACT FROM AUTHOR]

Imaging local magnetic fields produced by nano- and micrometer-scale superconductors has become a vital tool that can not only reveal crucial information on the vortex dynamics and order parameters of the superconducting materials but also visualize the working mechanism of superconducting devices made for quantum information. Here, we performed measurements of the magnetic field distributions of mesoscopic superconducting structures with various geometries by combining a thin ferromagnetic metal layer as a magneto-optical sensing element that responds to the environmental magnetic fields and a custom-made sensitive Sagnac interferometer. The sensitivity of the technique enables the observation of magnetic flux jumps due to individual vortex entries into nanostructured superconductors. In addition, with the control of incident power at a focused laser spot, we induce thermally driven movement of vortices that leaves a trace of a microscopic optical heating pattern. [ABSTRACT FROM AUTHOR]

All superconductors in a magnetic field are characterized by three critical magnetic fields: lower critical H c 1 , upper critical H c 2 and thermodynamic critical field H c . Only two sets of inequalities H c 2 > H c > H c 1 or H c 1 > H c > H c 2 are possible in a single-component superconductor. Here, we report our study of the critical fields in multicomponent superconductors with two superconducting components in the framework of the Ginzburg-Landau functional. We derive the relationship between the phases of the components of the superconducting complex order parameter from the charge conservation law in explicit form and insert it into the Ginzburg-Landau functional. Using the modified Ginzburg-Landau equation, we acquire the single vortex state including the analytical expression for asymptotics. Also, we obtain the analytical form for the state in the upper critical field. We find that in some cases an unusual sequence of critical fields H c 1 , H c 2 > H c can be realized in multicomponent superconductors. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have gained increasing prominence not only in fundamental research but also in daily applications. However, to fully harness their potential, it is crucial to optimize their properties with an external parameter and track the electronic structure simultaneously. Magnetotransport over a wide magnetic field range is a powerful method to probe the electronic structure and, for metallic 2D materials, quantum oscillations superimposed on the transport signals encode Fermi surface parameters. In this manuscript, we utilize biaxial strain as an external tuning parameter and investigate the effects of strain on the electronic properties of two quasi-2D superconductors, MoTe2 and RbV3Sb5, by measuring their magnetoresistance in pulsed magnetic fields up to 60 T. With a careful selection of insulating substrates, we demonstrate the possibility of both the compressive and tensile biaxial strains imposed on MoTe2 and RbV3Sb5, respectively. For both systems, the applied strain has led to superconducting critical temperature enhancement compared to their free-standing counterparts, proving the effectiveness of this biaxial strain method at cryogenic temperatures. Clear quantum oscillations in the magnetoresistance—the Shubnikov–de Haas (SdH) effect—are obtained in both samples. In strained MoTe2, the magnetoresistance exhibits a nearly quadratic dependence on the magnetic field and remains non-saturating even at the highest field, whereas in strained RbV3Sb5, two SdH frequencies showed a substantial enhancement in effective mass values, hinting at a possible enhancement of charge fluctuations. Our results demonstrate that combining biaxial strain and pulsed magnetic field paves the way for studying 2D materials under unprecedented conditions. [ABSTRACT FROM AUTHOR]

In this paper, we analyze in detail the features of the application of the magneto-optical imaging technique for studying HTS tapes. We present a detailed description of the experimental technique and features of the research facility for low temperatures research. The features of the penetration of a magnetic field into a superconductor are described, and the procedure for calibrating a magneto-optical film and algorithms for calculating magnetic field profiles from magneto-optical images are described in detail. [ABSTRACT FROM AUTHOR]

In this study, for the first time, we present a systematic study of the critical current density Jc at two magnetic field orientations and in a single crystal of the superconducting pnictide EuCsFe4As4, which shows a magnetic ordering below Tc and belongs to the 1144 family. The anisotropy of Jc and its temperature dependence are determined. The exponents of the dependences from 0.1 to 1 T are in a good agreement with the theoretical predictions for strong Abrikosov vortex pinning, which is also confirmed by the values of the pinning strength estimated using the Dew-Hughes model. [ABSTRACT FROM AUTHOR]

New concepts for Tokamak fusion reactors are enabled by ReBCO high temperature superconductors, either to achieve toroidal magnetic fields in the range of 20 T, and/or by operating temperatures above 4.2 K, e.g., 20 K. The application of ReBCO tapes is challenging because common techniques for the manufacturing and quench protection of magnets, developed for classical multifilamentary superconductors, such as NbTi and Nb3Sn, cannot be applied directly. Less risky would be the use of a ternary molybdenum chalcogenide (TMC) superconductor, which was under development before the discovery of high temperature superconductors. Although a low temperature superconductor, the upper critical field is extremely high resulting in a comparable field dependence of the critical current to ReBCO. Because of the improved superconductor fraction of a multifilamentary TMC conductor, the expected engineering current density can be one order of magnitude higher. In addition, a TMC conductor has the potential for cost efficiency and a performance index around 1 $/kAm at 20 T seems be possible. [ABSTRACT FROM AUTHOR]

The critical current density (Jc) of a superconductor with a high transition temperature is a fundamental quantity that determines the scope of the application of new superconductors in practice. Reports show that the critical transport current density of thin films of yttrium-based superconductors grown by different methods can range from the value106A/cm2' in temperature77k° to a value of the 107A/cm²order of4 ko. These values of current density provide the use of superconductors on a small scale in the electronic industry In this work, the dependence of the critical transfer current density of type II flat superconductor with a rectangular cross-section that is mixed in three magnetic fields that are applied perpendicular to the surface of the superconducting strip is investigated. The results of these calculations clearly show that (a)- as the thickness of the superconducting sample increases, the critical current density decreases (b)- the comparison of the results of the calculations of the application of three different fields indicates that with the increase of the field, it decreases. [ABSTRACT FROM AUTHOR]

In this study, for the first time, we present a systematic study of the critical current density Jc at two magnetic field orientations and in a single crystal of the superconducting pnictide EuCsFe4As4, which shows a magnetic ordering below Tc and belongs to the 1144 family. The anisotropy of Jc and its temperature dependence are determined. The exponents of the dependences from 0.1 to 1 T are in a good agreement with the theoretical predictions for strong Abrikosov vortex pinning, which is also confirmed by the values of the pinning strength estimated using the Dew-Hughes model. [ABSTRACT FROM AUTHOR]

In principle, high-temperature superconducting (HTS) flux-pinning maglev has the advantage of self-stable levitation and is therefore a good development prospect as a new rail transit technology. The magnetic field intensity is one of the key factors affecting the levitation performance of single-grain bulk superconductors in the HTS maglev system. To date, however, most researchers have focused on the levitation performance of HTS bulk superconductors in magnetic fields within a permanent magnet guideway (PMG) configuration. The magnitude of the external working magnetic field provided by a PMG is limited to about 0.5 T at 77 K, given that the superconductor usually levitates at a typical working height of 10 mm above the PMG. Therefore, the weak magnetic fields generated by the PMG significantly limits the levitation performance of HTS maglev systems to that of the permanent magnet (PM). In this article, a superconducting magnet test bench was utilized to provide a 0–3 T external magnetic field (B) environment for the study of the levitation force in HTS single grains. The difference in levitation performance between YBaCuO (YBCO) and GdBaCuO-Ag (GdBCO-Ag) bulk superconductors under large, changing magnetic fields was studied systematically. The relationships between levitation force and magnetic field characteristics, including vertical magnetic field component (Bz), transverse magnetic field component (Br), and vertical magnetic field variation (ΔBz) were investigated. The result of variation curves about YBCO and GdBCO bulks' levitation forces under different ΔBz shows that the levitation force of the bulk, single-grain superconductors will reach saturation under a varying ΔBz environment (0.72 and 1.5 T). The values of ΔBz corresponding to the saturation positions are found to be independent of the sizes of the HTS samples. At the same time, GdBCO-Ag exhibits a levitation force that is 112.8% greater than YBCO in B = 3 T magnetic environment. As a result, it is demonstrated that the levitation potential of single-grain HTS bulks can be better exploited by optimizing the distribution of the magnetic field. [ABSTRACT FROM AUTHOR]

Field-induced superconductivity is a rare phenomenon where an applied magnetic field enhances or induces superconductivity. Here, we use applied stress as a control switch between a field-tunable superconducting state and a robust non-field-tunable state. This marks the first demonstration of a strain-tunable superconducting spin valve with infinite magnetoresistance. We combine tunable uniaxial stress and applied magnetic field on the ferromagnetic superconductor Eu(Fe0.88Co0.12)2As2 to shift the field-induced zero-resistance temperature between 4 K and a record-high value of 10 K. We use x-ray diffraction and spectroscopy measurements under stress and field to reveal that strain tuning of the nematic order and field tuning of the ferromagnetism act as independent control parameters of the superconductivity. Combining comprehensive measurements with DFT calculations, we propose that field-induced superconductivity arises from a novel mechanism, namely, the uniquely dominant effect of the Eu dipolar field when the exchange field splitting is nearly zero. [ABSTRACT FROM AUTHOR]

Superconductor Nb open nanotubes are analyzed under a strong transport current in an external magnetic field using the time‐dependent Ginzburg–Landau equations. The geometric properties of the hysteresis loop in current–voltage characteristics are described for nanotubes of different radii from 190 to 440 nm as a function of the magnetic field. The hysteresis effect appears at a constant temperature as a result of the order parameter dynamics. In nanotubes of radii equal to 240 nm and larger, the area of the hysteresis loop manifests a non‐monotonic behavior as a function of the external magnetic field with a maximum ranging from 15 to 20 mT. Normal conductivity is shown to have a crucial impact on the hysteresis effect in superconductor open nanotubes. Namely, a higher normal conductivity leads to the disappearance of the hysteresis effect. As a rule, the upper and lower branches of the hysteresis loop are provided by the phase‐slip and vortex regimes, correspondingly. Just before the transition of the system from the upper branch to the lower one, the way of nucleation and annihilation of vortices in the region with suppressed superconductivity experiences readjustment. [ABSTRACT FROM AUTHOR]

We have studied how substitutions of magnetic Ni and nonmagnetic Zn in copper sites of Y3Ba5Cu8O18–δ (Y-358) affect critical temperature and the nonlinear behavior of current–voltage (IV) characteristics in the zero magnetic field. An exponent as a function of temperature (T) has been extracted to understand nonlinearity of IV within the framework of the BKT transition. We have extracted superfluid phase stiffness as a function of T of both groups of samples using the nonlinear exponent and the Ambegaokar–Halperin–Nelson–Siggia (AHNS) theory. The linear nature of the suppression of the critical temperature by Zn is found to be stronger than that of Ni. A strong suppression of the superfluid phase stiffness (SPS) by both dopants has also been observed. However, the suppression of the SPS with T by the nonmagnetic Zn is entirely different in comparison with the nonlinear suppression by the magnetic Ni. [ABSTRACT FROM AUTHOR]

Multi-phase flow hydrodynamics is an essential theoretical foundation for modernizing engineering and is important in guiding and developing modernizing engineering. In the realm of superconducting power technology, it is imperative to submerge and cool high-field superconducting magnets and superconducting cables, constructed from superconducting materials, in cryogenic fluids in order to maintain a superconducting state. Even minor thermal disturbances can induce boiling of the cryogenic fluid, leading to a two-phase flow regime. In the case of high-field superconducting magnets, the presence of liquid helium as the cooling medium gives rise to a diamagnetic effect. Consequently, the formation of a bubble resulting from boiling is confined in close proximity to the central aperture of the magnet owing to the influence of the magnetic field force. This confinement adversely affects the heat transmission properties of the magnet. This work presents a comprehensive analysis of the flow state during the boiling process of liquid helium, using the finite element approach and the mixture model. The heat transfer in a two-phase flow is analyzed by treating the system as a single pseudo-fluid. The model is consistent with empirical formulations of liquid helium boiling in large vessels and is also suitable for modeling the effect of heating surface orientation on the critical heat flux. Consequently, the analysis of the retention of helium bubbles generated by boiling in a high-field magnet has been further examined, using this particular model. The results of numerical hydrodynamic studies show that the width of the helium bubble stagnation zone is larger compared to the results of hydrostatic calculations. This poses a major challenge for superconducting magnets operating at high magnetic fields and high temperatures. The paper further analyses the effect of supercooled liquid helium on helium bubble stagnation, thus providing valuable insight into the construction of superconducting magnets with high magnetic fields. [ABSTRACT FROM AUTHOR]

The chemical interaction of Sn with H2 by X‐ray diffraction methods at pressures of 180–210 GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below TC = 72 K is obtained; the formation of a high molecular C2/m‐SnH14 superhydride and several lower hydrides, fcc SnH2, and C2‐Sn12H18, is also detected. The temperature dependence of critical current density JC(T) in SnH4 yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH4 has unusual behavior in strong magnetic fields: B,T‐linear dependences of magnetoresistance and the upper critical magnetic field BC2(T) ∝ (TC – T). The latter contradicts the Wertheimer–Helfand–Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non‐superconducting state exhibits a deviation from what is expected for phonon‐mediated scattering described by the Bloch‐Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed. [ABSTRACT FROM AUTHOR]

The chemical interaction of Sn with H2 by X‐ray diffraction methods at pressures of 180–210 GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below TC = 72 K is obtained; the formation of a high molecular C2/m‐SnH14 superhydride and several lower hydrides, fcc SnH2, and C2‐Sn12H18, is also detected. The temperature dependence of critical current density JC(T) in SnH4 yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH4 has unusual behavior in strong magnetic fields: B,T‐linear dependences of magnetoresistance and the upper critical magnetic field BC2(T) ∝ (TC – T). The latter contradicts the Wertheimer–Helfand–Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non‐superconducting state exhibits a deviation from what is expected for phonon‐mediated scattering described by the Bloch‐Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed. [ABSTRACT FROM AUTHOR]

On the recent report of a field-induced first order transition in the superconducting state of CeRh2As2, which is a possible indication of a parity-switching transition of the superconductor, the microscopic physics is still under investigation. However, if two competing paring channels of opposite parities do exist, a particle-particle collective mode referred to as the Bardasis-Schrieffer (BS) mode should generically exist below the pair-breaking continuum. The BS mode of the CeRh2As2 superconductor can couple to the light, as it arises from a pairing channel with the parity opposite to that of the superconducting condensate. Here, by using a generic model Hamiltonian we carry out a qualitative investigation on the excitation energy of the BS mode with respect to the out-of-plane magnetic fields and its contribution to the optical conductivity. Our findings indicate that the distinct coupling between the BS mode and the light can serve as evidence for the competing odd-parity channels of CeRh2As2 and other locally non-centrosymmetric superconductors. Superconductors with odd-parity Cooper pairs are rare and their experimental confirmation is significantly challenging. In the CeRh2As2 superconductor, the authors' investigation reveals that the presence of competing pairings with opposite parities gives rise to a unique collective mode, which can be observed through the optical response. [ABSTRACT FROM AUTHOR]

This research work focuses on the theoretical investigation of upper critical magnetic field ( H C 2 ), lower critical magnetic field ( H C 1 ), Ginzburg-Landau coherence length ( ξ GL ) and Ginzburg-Landau penetration depth ( λ GL ) in two-band model for the copper-based superconductors YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 . By employing the phenomenological Ginzburg-Landau (GL) free energy density functional theory in two-band model in the presence of two superconducting order parameters, we obtained the mathematical expressions for the temperature dependence of the upper critical magnetic field ( H C 2 (T) ) and lower critical magnetic field ( H C 1 (T) ); the angular dependence of upper critical magnetic field, H C 2 (θ) ; the temperature dependence of GL coherence length, ξ GL (T) and GL penetration depth, λ GL (T) for the superconductors YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 . By using the experimental values in the obtained expressions, the phase diagrams for the temperature dependence of upper critical magnetic fields parallel, H C 2 ‖ c (T) and perpendicular, H C 2 ⊥ c (T) to the crystallographic c-axis are plotted for YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 . Similarly, using the obtained expressions the phase diagrams for the angular dependence of upper critical magnetic field, H C 2 (θ) are plotted for YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 . We demonstrated that, the upper critical magnetic field along the ab-plane is greater than along the crystallographic c-axis for both YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 . We have also plotted the phase diagrams for the temperature dependence of lower critical magnetic fields parallel, H C 1 ‖ c (T) and perpendicular, H C 1 ⊥ c (T) to the crystallographic c-axis for the two copper-based superconductors. Moreover, the phase diagrams for the temperature dependence of GL coherence lengths in the ab-plane, ξ GL ab (T) and along the c-axis, ξ GL c (T) are plotted. Furthermore, we have plotted the phase diagrams for the temperature dependence of GL penetration depths in the ab-plane, λ GL ab (T) and along the c-axis, λ GL c (T) . Finally, the phase diagrams for the GL characteristic parameters, κ GL c and κ GL ab are plotted and the large values indicate that, YBa 2 Cu 4 O 8 and Bi 2 Sr 2 CaCu 2 O 8 are extreme type-II copper-based superconductors. The results we obtained in this research work are in broad agreement with previous experimental findings. [ABSTRACT FROM AUTHOR]

In the framework of the London model, a computer simulation has been performed and the magnetic field distribution in a thin film of type II superconductor has been found, taking into account changes in the magnetic field inhomogeneity of the irregular vortex lattice. It is shown that the line shape changes significantly depending on the vortex lattice irregularity. This change should be taken into account when interpreting the experimental data on the observation of the local magnetic field; consideration of this circumstance can change the conclusions regarding the type of vortex lattice and the parameters of the superconductor. [ABSTRACT FROM AUTHOR]

Some times ago, in the framework of the Boltzmann kinetic equation in the so-called τ -approximation, it was shown that perpendicular resistivity in quasi-two-dimensional (Q2D) conductors can be impurity independent in a broad range of high parallel magnetic fields [A. G. Lebed and N. N. Bagmet, Phys. Rev. B 55 (1997) R8654]. In this paper, we demonstrate that this result is much more general than the Boltzmann kinetic equation in the τ -approximation and is valid in a pure Q2D metal at low frequencies of the electric field. The above-mentioned statement open possibilities to test the above discussed phenomenon in a number of Q2D organic, high-Tc, and some other Q2D superconductors in their metallic phases and gives a method to extract some important information about their Q2D Fermi surfaces. [ABSTRACT FROM AUTHOR]

Both the transport critical current density at the zero magnetic field and magnetic critical current density in a composite system consisting of bulk YBCO superconductor and insulating BaTiO3 (BTO) have been studied using current–voltage (IV) and magnetization (M) as a function of magnetic field (H), respectively. Vortex pinning by insulating nanoparticles of BTO from the inter-granular network is investigated up to the magnetic field of 7.0 T. By analyzing magnetic critical current density the possibility of crossover from collective pinning (CP) to strong pinning (SP) and how it is affected by BTO have been explored based on the framework of Larkin–Ovchinnikov (LO) theory. Possible scenario of the strong pinning (SP) induced by insulating nanoparticles has also been studied using an exponent. [ABSTRACT FROM AUTHOR]

The existence of antiferromagnetism in rare-earth superconductors exhibits varieties of new physical phenomena. Experiments have highlighted the magnetic specific heat anomalies in antiferromagnetic superconductor. Structured around a Ginzburg-Landau theory, this article presents the role of magnetic field on the specific heat near the antiferromagnetic superconductor phase to normal state phase transition in rare-earth superconductors. The magnetic specific heat is calculated both at the antiferromagnetic superconductor phase and normal state. The qualitative agreement between theory and experiment is discussed. [ABSTRACT FROM AUTHOR]

Granular high-temperature superconductors (HTSs) are characterized by the hysteretic field dependences of magnetoresistance R(H) and critical current IC(H). These hysteretic effects are described within the concept of an effective field in the intergrain medium. The effective field is a superposition of external magnetic field H and the field induced by the magnetic moments of superconducting grains into intergrain spacings (grain boundaries). The magnetization of superconducting grains is determined by two contributions: Meissner (shielding) currents (MC) and trapped magnetic fluxes (Abrikosov vortices (AV)). To develop the concept of an effective field in the intergrain medium, the magnetotransport properties (R and IC) have been compared for two cases: (AV) the magnetization of superconducting grains is only determined by the trapped magnetic flux (zero external field) and (MC) HTS grains are in the Meissner state (the external field is weaker than the first critical field of grains). In a set of experiments, the main features of the hysteretic R(H) and M(H) dependences have been illustrated and the external conditions for implementing the AV and MC states have been established. It has been found that the effects of the Abrikosov vortices and intragrain Meissner currents on an effective field in the intergrain medium at the same magnetization values are noticeably different. This is a nontrivial fact that requires a thorough study of the impact of the anisotropy of the superconducting properties of grains on the configuration of the Meissner currents in them, as well as on the orientation of vortices both inside grains and near their surface. We suggest the explanation of observed stronger effect of the Meissner currents on the intergrain medium as compared with the effect of the Abrikosov vortices. [ABSTRACT FROM AUTHOR]

Transport characteristics of superconducting MoN strips with a single side cut near one of the superconductor edges in zero and weak magnetic fields are studied experimentally and theoretically. The presence of the cut makes it possible to observe regimes with one and several simultaneously moving Abrikosov vortices, the number of which is controlled by the value of the applied current. A change in the number of vortices is accompanied with the emergence of a "kink" on the current–voltage characteristic, which can be clearly distinguished in the dependence of the differential resistance on the current. This makes it possible to find average velocity of vortices (including a single vortex) and the current/voltage ranges with the known number of moving vortices. The vortex velocity determined in this way for our superconducting strips turns out to be weakly depending on the current and is close to maximal value ≈ 3 km/s, for which a superconductor transition to the normal state occurs. The maximal velocity value is comparable with the known values for superconductors of types Nb, NbN as well as, and YBCO, but is several times smaller than for superconductors of types MoSi, NbC, and Pb. The fact that difference in the maximal velocities of vortices is associated with different times of variation of the superconducting order parameter magnitude in different superconducting materials is considered. [ABSTRACT FROM AUTHOR]

Presently, magnetic resonance imaging (MRI) magnets must deliver excellent magnetic field (B0) uniformity to achieve optimum image quality. Long magnets can satisfy the homogeneity requirements but require considerable superconducting material. These designs result in large, heavy, and costly systems that aggravate as field strength increases. Furthermore, the tight temperature tolerance of niobium titanium magnets adds instability to the system and requires operation at liquid helium temperature. These issues are crucial factors in the disparity of MR density and field strength use across the globe. Low‐income settings show reduced access to MRI, especially to high field strengths. This article summarizes the proposed modifications to MRI superconducting magnet design and their impact on accessibility, including compact, reduced liquid helium, and specialty systems. Reducing the amount of superconductor inevitably entails shrinking the magnet size, resulting in higher field inhomogeneity. This work also reviews the state‐of‐the‐art imaging and reconstruction methods to overcome this issue. Finally, we summarize the current and future challenges and opportunities in the design of accessible MRI. [ABSTRACT FROM AUTHOR]

We perform the wavepacket dynamics simulation of a graphene-based device where propagating electron trajectories are tamed by an applied magnetic field toward a normal/superconductor interface. The magnetic field controls the incidence angle of the incoming electronic wavepacket at the interface, which results in the tunable electron–hole ratio in the reflected wave function due to the angular dependence of the Andreev reflection. Here, mapped control of the quasiparticle trajectories by the external magnetic field not only defines an experimental probe for fundamental studies of the Andreev reflection in graphene but also lays the foundation for further development of magnetic focusing devices based on nanoengineered superconducting two-dimensional materials. [ABSTRACT FROM AUTHOR]