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Superconducting phase transitions in two dimensions lie beyond the description of the Ginzburg-Landau symmetry-breaking paradigm for three-dimensional superconductors. They are Berezinskii-Kosterlitz-Thouless (BKT) transitions of paired-electron condensate driven by the unbinding of topological excitations, i.e. vortices. The recently discovered monolayers of layered high-transition-temperature (⁠|${{{T}}}_{{\rm C}}$|⁠) cuprate superconductor Bi2Sr2CaCu2O8+δ (Bi2212) meant that this 2D superconductor promised to be ideal for the study of unconventional superconductivity. But inhomogeneity posed challenges for distinguishing BKT physics from charge correlations in this material. Here, we utilize the phase sensitivity of scanning superconducting quantum interference device microscopy susceptometry to image the local magnetic response of underdoped Bi2212 from the monolayer to the bulk throughout its phase transition. The monolayer segregates into domains with independent phases at elevated temperatures below |${{{T}}}_{{\rm C}}$|⁠. Within a single domain, we find that the susceptibility oscillates with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up to |${{{T}}}_{{\rm C}}$|⁠. The finite modulation period, as well as the broadening of the peaks when approaching |${{{T}}}_{{\rm C}}$| from below, suggests well-defined vortices that are increasingly screened by the dissociation of vortex-antivortex plasma through a BKT transition. In the multilayers, the susceptibility oscillation differs in a small temperature regime below |${{{T}}}_{{\rm C}}$|⁠ , consistent with a dimensional crossover led by interlayer coupling. Serving as strong evidence for BKT transition in the bulk, we observe a sharp jump in phase stiffness and paramagnetism at small fields just below |${{{T}}}_{{\rm C}}$|⁠. These results unify the superconducting phase transitions from the monolayer to the bulk underdoped Bi2212, and can be collectively referred to as the BKT transition with interlayer coupling. [ABSTRACT FROM AUTHOR]

Considerations on the current status of the theory of superconductivity, the bibliometric H-index, and H. C. Andersen's tale about the emperor's new clothes. First appeared in the APS Forum on Physics and Society quarterly newsletter, January 2020. [ABSTRACT FROM AUTHOR]

We explore the state of matter characterized by the charged timelike vector order parameter. We employ holographic duality in order to construct such a state and study its thermoelectric transport, fermionic spectral function and the character of the Meissner effect. We uncover the unusual features of this "timelike superconductor": the absence of the gap in the fermionic spectrum and co-existence of Drude peak and supercurrent in the AC transport, which are reminiscent to those of time-reversal-odd and gapless superconductors, correspondingly. We show that this state is dynamically stable and thermodynamically at least metastable. Along the way we develop the holographic model of the charged vector field, which acquires mass due to a variant of the Stueckelberg mechanism with the adjoint Higgs field. [ABSTRACT FROM AUTHOR]

An attempt is made to describe from first principles the large-scale structure of the confining vacuum in quantum chromodynamics. Starting from our previous variational studies of the SU(2) pure gauge theory in an external Abelian chromomagnetic field and extending Feynman's qualitative analysis in (2+1)-dimensional SU(2) gauge theory, we show that the SU(3) vacuum in three-space and one-time dimensions behaves like a disordered chromomagnetic condensate. Color confinement is assured by the presence of a mass gap together with the absence of color long-range correlations. We offer a clear physical picture for the formation of the flux tube between static quark charges that allows us to determine the color structure and the transverse profile of the flux-tube chromoelectric field. The transverse profile of the flux-tube chromoelectric field turns out to be in reasonable agreement with lattice data. We, also, show that our quantum vacuum allows for both the color and ordinary Meissner effect. We find that for massless quarks, the quantum vacuum can accommodate a finite non-zero density of fermion zero modes leading to the dynamical breaking of the chiral symmetry. [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]

In a classic paper of 1960, W. H. Cherry and J. I. Gittleman discussed various thermal and electrodynamic aspects of the superconductive transition process relevant to practical applications. In a section of the paper that has remained unnoticed, they proposed a physical model for the Meissner effect. Earlier in 1940–1943, in work that has also remained unnoticed, K. M. Koch had introduced related physical ideas to explain the Meissner effect. Still earlier in 1937, J. C. Slater proposed a model to explain the perfect diamagnetism of superconductors. None of these ideas are part of the conventional London-BCS understanding of superconductivity, yet I will argue that they are essential to understand the Meissner effect, the most fundamental property of superconductors. The unconventional theory of hole superconductivity unifies and extends these ideas. A key missing element in the conventional theory as well as in these early theories is electron-hole asymmetry. A proper understanding of the Meissner effect may help with practical applications of superconductors, as well as to find new superconducting materials with desirable properties. [ABSTRACT FROM AUTHOR]

Superconducting materials exhibit unique physical properties and have great scientific value and vast industrial application prospects. However, due to limitations, such as the critical temperature (TC) and critical current density (JC), the large-scale application of superconducting materials remains challenging. Chemical doping has been a commonly used method to enhance the superconductivity of B(P)SCCO. However, satisfactory enhancement results have been difficult to achieve. In this study, we introduce green-light GaN p-n junction particles as inhomogeneous phases into B(P)SCCO polycrystalline particles to form a smart meta-superconductor (SMSC) structure. Based on the electroluminescence properties of the p-n junction, the Cooper pairs were stimulated and strengthened to enhance the superconductivity of B(P)SCCO. The experimental results demonstrate that the introduction of inhomogeneous phases can indeed enhance the critical temperature TC, critical current density JC, and complete diamagnetism (Meissner effect) of B(P)SCCO superconductors. Moreover, when the particle size of the raw material of B(P)SCCO is reduced from 30 to 5 μm, the grain size of the sintered samples also decreases, and the optimal doping concentration of the inhomogeneous phases increases from 0.15 wt.% to 0.2 wt.%, further improving the superconductivity. [ABSTRACT FROM AUTHOR]

Under the spell of BCS-electron–phonon theory [M. Tinkham, Introduction to Superconductivity, 2nd ed. (McGraw Hill, New York, 1996)], during the last 6 years experimentalists have purportedly discovered a plethora of high temperature conventional superconductors among pressurized hydrides [Pickard et al., Ann. Rev. Condens. Matter Phys. 11, 57 (2020) and R. F. Service, Science 373, 954 (2021)], and theorists have been busy predicting and explaining those findings [Lv et al., Matter Radiat. Extremes 5, 068101 (2020); Flores-Livas et al., Phys. Rep. 856, 1 (2020); and Boeri et al., J. Phys. Condens. Matter. (to be published)]. The alternative theory of hole superconductivity (see https://jorge.physics.ucsd.edu/hole.html for a list of references) predicts instead that no superconductivity can exist in these materials. In this Tutorial, I will first argue that, unclouded by the prejudice of BCS's validity, the existing experimental evidence for superconductivity in pressurized hydrides does not withstand scrutiny. Once it is established that superconductivity in pressurized hydrides is a myth and not a reality, the claim to validity of BCS-electron–phonon theory as a descriptor of superconductivity of real materials will be forever shattered, and an alternative theory will become imperative. I will explain the fundamentals of the theory of hole superconductivity, developed over the past 32 years [see https://jorge.physics.ucsd.edu/hole.html and J. E. Hirsch, Phys. Lett. A 134, 451 (1989)], and why it is compelling. Crucially, it explains the Meissner effect, that I argue the conventional theory does not. It applies to all superconducting materials and provides guidelines in the search for high temperature superconductors that are very different from those provided by BCS-electron–phonon theory. Light elements are predicted to be irrelevant to warm superconductivity because according to this theory the electron–phonon interaction plays no role in superconductivity. [ABSTRACT FROM AUTHOR]

Superconductors are materials with zero electrical resistivity and the ability to expel magnetic fields, which is known as the Meissner effect. Their dissipationless diamagnetic response is central to magnetic levitation and circuits such as quantum interference devices. In this work, we used superconducting diamagnetism to shape the magnetic environment governing the transport of spin waves—collective spin excitations in magnets that are promising on-chip signal carriers—in a thin-film magnet. Using diamond-based magnetic imaging, we observed hybridized spin-wave– Meissner-current transport modes with strongly altered, temperature-tunable wavelengths and then demonstrated local control of spin-wave refraction using a focused laser. Our results demonstrate the versatility of superconductor-manipulated spin-wave transport and have potential applications in spin-wave gratings, filters, crystals, and cavities. [ABSTRACT FROM AUTHOR]

The article reports on a universal mechanism for the Josephson diode effect in short Josephson junctions, which is attributed to finite Cooper pair momentum and simultaneous breaking of inversion and time-reversal symmetries, resulting in a diode efficiency of up to 40%. This mechanism expands the platforms for observing super current diode effects without relying on spin-orbit coupling.

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]

The electronically nematic order has emerged as a key feature of cuprate superconductors, however, its correlation with the fundamental properties such as the electromagnetic response remains unclear. Here the nematic-order state strength dependence of the electromagnetic response in cuprate superconductors is investigated within the framework of the kinetic-energy-driven superconductivity. It is shown that a significant anisotropy of the electromagnetic response is caused by the electronic nematicity. In particular, in addition to the pure d-wave component of the superconducting gap, the pure s-wave component of the superconducting gap is generated by the electronic nematicity, therefore there is a coexistence and competition of the d-wave component and the s-wave component. This coexistence and competition leads to that the maximal condensation energy appears at around the optimal strength of the electronic nematicity, and then decreases in both the weak and strong strength regions, which in turn induces the enhancement of superconductivity, and gives rise to the dome-like shape of the nematic-order state strength dependence of the superfluid density. [ABSTRACT FROM AUTHOR]

The penetration depth is a magnetic field mechanism by which an external magnetic field penetrates into superconductors' surfaces and is related to the Meissner effect. The penetration depth property was studied by the semiclassical approach to identify other properties of superconductors. In this study, we investigated the penetration depth of the H3S superconductor under external pressure. The H3S superconductor is high Tc, s-wave isotropic, and high pressure prepared superconductors. We derive an analytical equation for the near-zero temperature penetration depth with pressure effect parameters. The derived equations were then numerically calculated and predicted the experimental data on H3S superconductor penetration depth. We discovered that the temperature dependent penetration depth under pressure of H3S superconductor is reasonable at Tc(χ = 473, ε0 = 91,Qp = 0.1) = 200.832 K., as well as is the influence of the directly χ parameter on Tc(χ,ε0, Qp), Δ(0,χ, ε0,Qp), and λ(T,χ,ε0,Qp), with Qp>0.1 does not corresponding theory [ABSTRACT FROM AUTHOR]

Compressed hydrogen-rich compounds have been verified extensively by theoretical scientists for finding high-temperature superconductivity. Although some experiments confirm these findings, their requirement of extremely high critical pressure condition ( 100 GPa ≲ P c ) makes them impossible to apply in daily life. The main purpose of present work is to help finding materials with high-temperature superconductivity at low pressures. For this purpose, we consider two graphene sheets with sine form corrugations whose honeycomb patterns are exactly on top of each other with some doped molecules intercalated into sheets. The free energy of valence electrons of total atoms is computed for doped molecules PrH 6 , PrH 7 , PrH 8 , and PrH 9 , separately. Our calculations indicate a second-order phase transition for PrH 9 at critical temperature T c = 179.01 K with applying no external pressure, while no phase transition is observed for other doped molecules. This high-temperature electronic structural stability is 46 K greater than the T c of the cuprate materials which are the highest-temperature superconductors at low pressures. We guess this phase transition is a superconductivity transition due to the observation of Meissner effect in magnetic susceptibility diagram. [ABSTRACT FROM AUTHOR]

When approaching extremality, rotating black holes tend to expel the magnetic field in which they are immersed. This phenomenon, being reminiscent of the Meissner-Ochsenfeld effect in superconductors, is known as the black hole Meissner effect, and here we study it in the backreacting regime and from the near horizon perspective. By resorting to methods recently developed in the literature, which allow to compute conserved charges in the near horizon region, regardless the details of the asymptotia at large distance, we investigate the properties of the black hole horizon when in its Meissner state. We show that, when in such state, the horizon exhibits two sets of supertranslation symmetries as well as a symmetry generated by the local conformal group. The supertranslations are generated by two infinite sets of currents, one of which comes from local dilations of the advanced null coordinate at the horizon, and the other from local gauge transformations that preserve the electromagnetic field configuration at the horizon. We show that the evaluation of the conserved charges associated to these symmetries correctly reproduce the physical charges of the magnetized black holes and their thermodynamics. This represents a concrete application of the techniques developed in [1–3] and it extends the results of [4] to arbitrary values of the black hole charges. In addition, we elaborate on the charges computation at the horizon: we show the equivalence between the horizon charges and the evaluation of the corresponding Komar integrals. Besides, we show the validity of the Gauss phenomenon by explicitly relating near horizon charges with fluxes and charges computed by other techniques. All this provides a method to derive the thermodynamics of magnetized horizons in a quite succinct way, including the case of horizons exhibiting the Meissner effect. [ABSTRACT FROM AUTHOR]

We investigate correspondence between the Melvin–Kerr–Newman–Taub–NUT spacetime, and the conformal field theory. The near horizon geometry of extremal Melvin–Kerr–Newman–Taub–NUT spacetime possesses the S L 2 , R × U 1 isometry, which allows one to employ the asymptotic symmetry group method, in establishing the holographic correspondence for the spacetime. We also use the alternative way of the stretched horizon method, to compute the extremal entropy of the black hole. We find perfect agreement between the results of asymptotic symmetry group and the stretched horizon methods, to establish the holography for the extremal Melvin–Kerr–Newman–Taub–NUT black hole. The black hole Meissner effect for the Melvin–Kerr–Taub–NUT black hole is also discussed. [ABSTRACT FROM AUTHOR]

Reference [1] presents evidence for magnetic field screening and "subtle" evidence for magnetic field expulsion in hydrides under high pressure, which is argued to support the claim that these materials are high temperature superconductors. We point out here that data presented in different figures of Ref. [1] are inconsistent (i) with one another, (ii) with other work by the same authors on the same samples [2-3], and (iii) with the expected behavior of standard superconductors. This suggests that these magnetic phenomena reported for these materials are not associated with superconductivity, undermining the claim that these materials are high temperature superconductors. [ABSTRACT FROM AUTHOR]

The accidental discovery of mercury's zero resistance at temperatures lower than 4.2 K which took place in 1911 by the Dutch physicist Heike Kamerlingh Onnes in his laboratory at the University of Leiden, appeared to be one of the greatest breakthroughs of physics of all time. It has led to the creation of an entirely new field within physics called superconductivity; this attracted many of the finest minds in physics whose work in this area produced no less than six Nobel Prizes to date. Zero resistance, together with the expulsion of magnetic fields which was discovered many years later, are the two unique and intriguing properties of superconductors which puzzled scientists' brains for a proper theoretical explanation of the observed phenomena. However in 1935, the phenomenological theory proposed by Fritz and Heinz London (known as the London theory) was the first success in the field, which was followed in the 1950s by another phenomenological theory put forward by Vitaly Ginzburg and Lev Landau. Despite this, a satisfactory microscopic theory for superconductivity had to wait until 1957 when John Bardeen, Leon Cooper and John Robert Schrieffer proposed their theory, which was nicknamed the BCS theory in their honour. The more recent discovery of the cuprate high temperature superconductors (HTS) in 1986 gave a new momentum to the field and intensified the search for room temperature superconductors which continues to this day. While this quest is under way, and new theories of superconductivity are being developed, physicists, material scientists and engineers are using superconductors to establish new technologies and build machines, devices and tools with unprecedented properties. Today superconductors are widely used in healthcare, particle accelerators, ultrasensitive instrumentation and microwave engineering and they are being developed for use in many other areas as well. In this review, we will trace the history of superconductors and provide a brief overview into some of the recent applications of superconductivity. [ABSTRACT FROM AUTHOR]

YBa 2 Cu 3 O y (Y-123) is one of the most intensively studied high-temperature superconductors (HTS) and has great potential for applications in electronics. Its superconducting properties significantly depend on the oxygen index (y), the peculiarities of the atomic crystal and microgranular structure, the type and concentration of contaminating atoms. Therefore, of particular interest are the techniques of HTS synthesis that significantly affect the superconducting properties, as well as modifications of these techniques. The aim of this study was to investigate the effect of ultrahigh dilution (UHD) technology on the Y-123 HTS properties. We applied UHD technology to treat Y 2 O 3 ·4BaO 2 ·6CuO composition (before and/or after calcination) and used solid-phase reaction to obtain batches of ceramic samples of the Y-123 phase. Main characteristics of the synthesized HTS specimens (the orthorhombic unit cell parameters, temperature dependence of electrical resistance, Meissner effect, and critical current density) were studied. X-ray phase analysis demonstrated that the samples were practically single-phase and consisted of the Y-123 phase. Depending on the treatment method, the modifying effect varied. Positive and most significant results were demonstrated for specimens obtained from precursor powder mixture treated with UHD. For some of such specimens an increase in the temperature of the beginning of the transition to the superconducting state by 3.8 K, the Meissner effect by 9%, and the density of the intergranular critical current by 35% were observed. We conclude that UHD technology can be used to improve properties of HTS. However, methodology for implementation of UHD technology should depend on which specific superconductor property needs to be changed. [ABSTRACT FROM AUTHOR]

In this study, an experimental design was employed to optimize the fabrication of the YCa 2 Cu 3 O 7 superconductor composite. The superconductors were fabricated using biocompatible calcium carbonate nanoparticles extracted from cuttlebone, Sepia pharaonis, of the Persian Gulf in the Bushehr coastal area, and their effects on YCa 2 Cu 3 O 7 superconductor's properties were investigated. Ball milling process and solid-state calcination reaction were used for obtaining the natural calcium carbonate nanoparticles and fabrication of the superconductors, respectively. The effects of three factors, milling time and the excess amount of the natural calcium carbonate as well as yttrium oxide, were investigated on the superconductivity properties of the products. The Taguchi statistical design of experiments was conducted to reveal the sensitivity analysis of the products' properties due to the variation in each variable, finding optimal production conditions, and reduction in the total number of required experiments. In this method, the oxygen content of the fabricated superconductor was considered as the targeted YCa 2 Cu 3 O 7 property. Moreover, the morphology and structural properties of the products were investigated to find the relationship between physicochemical properties and superconductivity. The YCa 2 Cu 3 O 7 superconductors were characterized by the Meissner effect test, XRD analysis, and FESEM imaging. The sensitivity analysis was shown that by increasing milling time and the excess amount of the reactants in the solid-state reaction, the connectivity and crystallization of the grains were improved, and the optimum operating conditions for the production were achieved. Besides, the variation in milling time causes more signal-to-noise ratio, which indicates the highest efficacy of this factor on the superconductivity of the products in comparison with the other variables. [ABSTRACT FROM AUTHOR]

Increasing and improving the critical transition temperature (TC), current density (JC) and the Meissner effect (HC) of conventional superconductors are the most important problems in superconductivity research, but progress has been slow for many years. In this study, by introducing the p-n junction nanostructured electroluminescent inhomogeneous phase with a red wavelength to realize energy injection, we found the improved property of smart meta-superconductors MgB2, the critical transition temperature TC increases by 0.8 K, the current density JC increases by 37%, and the diamagnetism of the Meissner effect HC also significantly improved, compared with pure MgB2. Compared with the previous yttrium oxide inhomogeneous phase, the p-n junction has a higher luminescence intensity, a longer stable life and simpler external field requirements. The coupling between superconducting electrons and surface plasmon polaritons may be explained by this phenomenon. The realization of smart meta-superconductor by the electroluminescent inhomogeneous phase provides a new way to improve the performance of superconductors. [ABSTRACT FROM AUTHOR]

In this paper we examine the mechanisms leading to thermomagnetic instability in nanostructured materials and study their regularities. The appearance of thermomagnetic instabilities in the superconducting state of various materials remains one of the problems of applications of superconductors. We studied the temperature and the magnetic field dependences of the magnetization m(T, H) and heat capacity C(T, H) of a nanocomposite consisting of interconnected lead filaments embedded in nanoporous glass (Pb-PG) with filament diameter d = 7 nm. Porous glass contains an arbitrarily orientated multiply connected system of pores of approximately the same size; lead in the nanocomposite forms a replica of the pore system. Thermomagnetic instability was previously observed in this material in superconducting state at T ≤ 5 K on m(H) dependencies in magnetization studies. We established that high enough external heater power P used during the heat capacity measurements in external magnetic field C(H) at T ≤ 5 K can initiate thermomagnetic instability and penetration of magnetic flux into the nanocomposite. The thermomagnetic instability is generally preceded by a sequence of small heat release events with the same magnitude as P. Another sequence of small heat release events is observed in the region close to H c2. These events are presumably linked to the thermomagnetic instability process and are caused by small redistribution of magnetic flux in the nanocomposite. [ABSTRACT FROM AUTHOR]

A few years later, thanks to a steadfast motivation, Francis started building a second-generation Cryopad at ILL and a first polarised SP 3 sp He filling station at Mainz University. With deep sadness, I announce the death of our friend and former colleague Francis Tasset on Thursday 20 April 2023. Francis leaving the JRR-3 reactor in 2003 after 5 weeks of intense work to successfully install the Cryopad on the TAS-1 three-axis spectrometer. [Extracted from the article]

The article presents a study which explores the Universal Josephson diode effect. It mentions the universal mechanism for the Josephson diode effect in short Josephson junctions. It discusses the scheme for achieving finite-momentum pairing, which does not rely on spin-orbit coupling and thus greatly expands existing platforms for the observation of supercurrent diode effects.

The temperature dependences of the longitudinal resistance and heat capacity of silicon-carbide epitaxial films grown on single-crystal silicon substrates by the method of ghe coordinated substitution of atoms are investigated. The features in the behavior of these dependences are found at temperatures of 56, 76, 122, and 130°C. The observed features of the behavior of the heat capacity and longitudinal resistance taking into account the appearance of a giant value of diamagnetism previously discovered in samples at these temperatures are interpreted as the phase transitions of charge carriers into a coherent (possibly superconducting if we take into account diamagnetism) state. [ABSTRACT FROM AUTHOR]

In recent years, the field of flexible electronics has become one of the cross-disciplinary research hotspots, attracting worldwide attention and making rapid advances. So far, there has been plenty of research on the use of two-dimensional (2D) materials in flexible electronics, including graphene, transition metal dichalcogenide, and so on. In this work, we successfully prepared quasi-one-dimensional (Q1D) Nb2Pd0.73S5.97 superconductors on flexible paper by mechanical friction and systematically studied their physical properties at low temperatures. Superconductivity with transition temperature (Tc) ∼ 6.05 K by Meissner effect was observed in Nb2Pd0.73S5.97 wires coated on flexible paper, and a resistance drop at 4.80 K was confirmed in electrical transport measurements. The lower critical field (Hc1) of coated paper shows anisotropy effect under parallel and perpendicular magnetic fields, exhibiting a 2D-like feature, unlike the bulk Nb2Pd0.73S5.97 fibers. Our work provides a broader platform for the application of low-dimensional materials in flexible functional devices. [ABSTRACT FROM AUTHOR]

Recently, it was claimed by King & Pringle that accretion of electric charge by a black hole (BH) rotating in an aligned external magnetic field results in a 'dead' vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford–Znajek mechanism cannot operate. Here, we study in details the properties of the Wald solution for electrically charged BHs discussed in their paper. Our results show that the claim is erroneous as in the solution with the critical charge q 0 = 2 aB 0, there exists a drop of electrostatic potential along all magnetic field lines except the one coinciding with the symmetry axis. It is also found that while uncharged rotating BHs expel external vacuum magnetic field from their event horizon (the Meissner effect), electric charging of BHs pulls the magnetic field lines back on it, resembling what has been observed in some previous force-free, Relativistic Magnetohydrodynamics (RMHD), and Particle-in-Cell (PIC) simulations of BH magnetospheres. This suggests that accretion of electric charge may indeed be a feature of the BH electrodynamics. However, our analysis shows that the value q 0 of the BH charge given by Wald is likely to be only an upper limit, and that the actual value depends of the details of the magnetospheric physics. [ABSTRACT FROM AUTHOR]

The current-carrying capacity of second-generation commercial high-temperature superconducting REBCO tapes with a width of 12 mm without a stabilizing copper coating (high-temperature superconductor (HTSC) tapes) in liquid helium has been experimentally investigated at current injection rates up to 350 kA/s. In the experiments, tape samples in the form of rings with junctions are placed in the working volume of a superconducting magnet at 4.2 K. The current in the samples is induced by the transformer method. With an increase in the rate of current injection in the ring-shaped samples, single mechanical defects of the superconducting layer appear in the region of junctions, which causes premature transitions of the samples to the normal state. As a result, the maximum attained currents in the ring samples turned out to be up to 50% lower than the critical currents of short HTSC tape samples at 4.2 K. In conclusion, the analysis of the experimental results is given. Possible explanations for the observed effect are given. In addition, the thermomagnetic stability of two single pancake coils comprised of five isolated turns wound from REBCO tapes supplied from different manufacturers is investigated. The jumps in the magnetic flux are not detected up to an external magnetic field variation rate of 1.7 T/s. [ABSTRACT FROM AUTHOR]

The dependence of magnetization M on magnetic field H was measured for a thin superconducting niobium plate with strong magnetic flux pinning with the field oriented normally and parallel to the sample plane. At T < Tc, dependences M(H) show a hysteretic behavior with a peak effect in large fields; the shape of the hysteresis loop depends on the field orientation. At temperatures below ~Tc/2 magnetic field jumps appear on dependences M(H), and their behavior also depends on the field orientation. When a good conductor is in the in a good thermal contact with the planar superconducting sample, the flux jumps are noticeably reduced in the perpendicular field orientation, while the flux jumps in the parallel orientation remain unchanged. The decrease in the magnitude of the flux jumps with a transverse orientation of the magnetic field occurs due to the electrodynamic braking of magnetic instability, which could lead to a magnetic flux jump. [ABSTRACT FROM AUTHOR]

We investigate the thermodynamics of two-flavor quark matter in presence of nonzero isospin chemical potential and external magnetic field. It is known that at sufficiently high isospin chemical potential, charged pions undergo Bose–Einstein condensation (BEC). The condensate behaves as a superconductor, exhibiting Meissner effect in weak external magnetic fields. Stronger fields stress the superconducting state, turning it first into an Abrikosov lattice of vortices, and eventually destroying the condensate altogether. On the other hand, for sufficiently strong magnetic fields and low-to-moderate isospin chemical potential, the ground state of quantum chromodynamics (QCD) is expected to be a spatially modulated condensate of neutral pions, induced by the chiral anomaly: the chiral soliton lattice (CSL). We map the phase diagram of QCD as a function of isospin chemical potential and magnetic field in the part of the parameter space accessible to a low-energy effective field theory description of QCD. Our main result is an explicit account of the competition between the CSL and the Abrikosov vortex lattice. This is accomplished by adopting a fast numerical algorithm for finding the vortex lattice solution of the equation of motion and the corresponding Gibbs energy. We find that the Abrikosov vortex lattice phase persists in the phase diagram, separating the uniform charged pion BEC phase from the CSL phase. The precise layout of the phase diagram depends sensitively on the choice of the vacuum pion mass. [ABSTRACT FROM AUTHOR]

Flux pinning of bulk YBa $_2$ Cu $_3$ O $_{7-\delta }$ (Y-123) superconductors is commonly done using secondary phase particles, mainly Y $_2$ BaCuO $_5$ (Y-211) particles, which are created during the growth of the samples or additionally added. However, the crystallographic parameters of Y-211 particles indicate a misfit to the ones of Y-123, there will be residual strain around such particles within the Y-123 matrix. Here, we perform a dedicated analysis of electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD) data obtained on various Y-123 superconductor samples (Y-123 bulks prepared by melt-texture, melt-growth and the infiltration growth, YBCO foam struts and commercial YBCO coated conductors). This enables the strain distribution around such embedded secondary phase particles to be revealed down to the nanometer scale. The results are presented in the form of Kernel Average Misorientation (KAM) mappings. Around large Y-211 particles and around clusters, the strain can be so large that even subgrains in the Y-123 matrix are formed. The impact of the strain distribution on the flux pinning properties is discussed, as stress/strain can deliver an extra source of flux pinning. Therefore, it is essential to properly control the particle size as well as their distribution within the bulk sample to achieve the best superconducting performance. [ABSTRACT FROM AUTHOR]

Prozorov and Bud'ko (On the analysis of the tin-inside-H3S Mössbauer experiment, 2022) recently analyzed the nuclear resonant scattering (NRS) experiment that reportedly demonstrated magnetic field exclusion in sulfur hydride under pressure (Science 351, 1303, 2016), and concluded that the experiment is consistent with the expected behavior of a type II superconductor. Here I point out that their analysis shows that the reported NRS measurements are incompatible with the recently reported magnetization measurements by Minkov et al. (Nat Commun 13, 3194, 2022), indicating that at minimum one of these two experiments does not support the claim that sulfur hydride under pressure is superconducting. [ABSTRACT FROM AUTHOR]

Bulk high-temperature superconductors are widely used in various superconducting devices for their high critical current density and the ability to trap large magnetic field. In some applications, bulk superconductors can be arranged in an array structure to increase the magnetic field strength. However, rectangular bulk superconductors can be arranged more compactly than commonly used cylindrical bulk superconductors. The unique shape of rectangular bulk superconductors results in different distributions of electromagnetic fields, temperature, and stress under a pulsed-field magnetization (PFM) than for cylindrical bulk superconductors. In bulk superconductors, growth sector boundaries and growth sector regions have different critical current density, resulting in an uneven critical current density. Therefore, in this study, the electromagnetic and mechanical behavior of non-uniform rectangular bulk superconductors during the PFM process is investigated. The corresponding distribution and variation in the magnetic field, current, temperature, and stress in the bulk are calculated and analyzed. The influence of rectangle aspect ratio on the electromagnetic and mechanical behavior is discussed. The calculation results show that the magnetic flux jumps occur accompanied by sudden changes in the temperature and pressure. The effect of the aspect ratio of rectangular bulk superconductors on their electromagnetic and mechanical properties is analyzed. The influence of preexisting cracks in a non-uniform rectangular bulk superconductor on the simulation results is discussed. The numerical results indicate that the presence of an edge crack exacerbates the magnetic flux jump as well as the jumps in the temperature and stress. However, a central crack has a relatively small effect on the stability of a bulk superconductor. [ABSTRACT FROM AUTHOR]

The paper reviews the latest advances in the growth of epitaxial SiC films on Si by the coordinated atomic substitution method. The conceptual issues and procedure of the new method for synthesizing epitaxial SiC films on Si are described. It is shown that this method significantly differs from the classical thin film growth schemes. Film growth in accordance with the classical mechanism is provided by deposition of atoms on the surface of a substrate. The new method consists in the coordinated atomic substitution of a portion of the atoms of the silicon matrix by carbon atoms to form an epitaxial silicon carbide film. The new growth method is compared with the classical thin film growth mechanisms. It is shown that the main distinctive feature of SiC films synthesized by this method is the formation of an excess concentration of silicon vacancies in it, whereas SiC grown by the standard methods comprises mostly carbon vacancies. It is shown that the interaction of carbon atoms and silicon vacancies leads to the formation of ordered ensembles of carbon–vacancy structures in SiC layers grown by the coordinated atomic substitution method. The formation of these structures is attributed to both the occurrence of a chemical substitution reaction and the contraction of the Si lattice cell during the transformation of it into a SiC lattice cell. The presence of carbon–vacancy structures in SiC imparts a number of new unique properties to the silicon carbide. In particular, a Si layer exhibiting the electronic properties of a "semimetal" is formed at the SiC–Si interface. In addition, carbon–vacancy structures provide unique optical, electrical, and magnetic properties. In particular, two quantum effects—a hysteresis of the static magnetic susceptibility and the occurrence of Aharonov–Bohm oscillations in the field dependences of the static magnetic susceptibility—are found to occur in weak magnetic fields at room temperature. The first of the effects is associated with the Meissner–Ochsenfeld effect; the second is associated with the presence of carbon–vacancy structures and microdefects in the form of nanotubes and micropores formed in these structures during SiC synthesis under the SiC layer. [ABSTRACT FROM AUTHOR]

The dependence of magnetization M on magnetic field H was measured for a thin superconducting niobium plate with strong magnetic flux pinning with the field oriented normally and parallel to the sample plane. At T < Tc, dependences M(H) show a hysteretic behavior with a peak effect in large fields; the shape of the hysteresis loop depends on the field orientation. At temperatures below ~Tc/2 magnetic field jumps appear on dependences M(H), and their behavior also depends on the field orientation. When a good conductor is in the in a good thermal contact with the planar superconducting sample, the flux jumps are noticeably reduced in the perpendicular field orientation, while the flux jumps in the parallel orientation remain unchanged. The decrease in the magnitude of the flux jumps with a transverse orientation of the magnetic field occurs due to the electrodynamic braking of magnetic instability, which could lead to a magnetic flux jump. [ABSTRACT FROM AUTHOR]

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7âˆ' x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180Âş with the layer plane. The value of the Curie temperature T Curie estimated using the Curieâ€"Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect. [ABSTRACT FROM AUTHOR]

The current-carrying capacity of second-generation commercial high-temperature superconducting REBCO tapes with a width of 12 mm without a stabilizing copper coating (high-temperature superconductor (HTSC) tapes) in liquid helium has been experimentally investigated at current injection rates up to 350 kA/s. In the experiments, tape samples in the form of rings with junctions are placed in the working volume of a superconducting magnet at 4.2 K. The current in the samples is induced by the transformer method. With an increase in the rate of current injection in the ring-shaped samples, single mechanical defects of the superconducting layer appear in the region of junctions, which causes premature transitions of the samples to the normal state. As a result, the maximum attained currents in the ring samples turned out to be up to 50% lower than the critical currents of short HTSC tape samples at 4.2 K. In conclusion, the analysis of the experimental results is given. Possible explanations for the observed effect are given. In addition, the thermomagnetic stability of two single pancake coils comprised of five isolated turns wound from REBCO tapes supplied from different manufacturers is investigated. The jumps in the magnetic flux are not detected up to an external magnetic field variation rate of 1.7 T/s. [ABSTRACT FROM AUTHOR]

We show that a ferromagnetic (F) slab with the in-plane magnetization sandwiched between two superconducting (S) films experiences strong demagnetization effect due to the Meissner screening of the stray magnetic field by superconductors. In the extreme case, the transition of the S film from normal to the superconducting state can switch the demagnetization factor from 0 to 1, which is in a sharp contrast with the S/F bilayers where such transition affects the magnetic field inside the F film only slightly. The giant demagnetization effect is shown to be qualitatively robust against the decreasing superconducting film thickness and may provide a hint toward the explanation of the anomalously large ferromagnetic resonance frequency shift recently observed for the S/F/S structures [Golovchanskiy et al., Phys. Rev. Appl. 14, 024086 (2020)]. [ABSTRACT FROM AUTHOR]

The discovery of the Meissner (Meissner–Ochsenfeld) effect in 1933 was an incontestable turning point in the history of superconductivity. First, it demonstrated that superconductivity is an unknown before equilibrium state of matter, thus allowing to use the power of thermodynamics for its study. This provided a justification for the two-fluid model of Gorter and Casimir, a seminal thermodynamic theory founded on a postulate of zero entropy of the superconducting (S) component of conduction electrons. Second, the Meissner effect demonstrated that, apart from zero electric resistivity, the S phase is also characterized by zero magnetic induction. The latter property is used as a basic postulate in the theory of F. and H. London, which underlies the understanding of electromagnetic properties of superconductors. Here the experimental and theoretical aspects of the Meissner effect are reviewed. The reader will see that, in spite of almost nine decades age, the London theory still contains questions, the answers to which can lead to a revision of the standard picture of the Meissner state (MS) and, if so, of other equilibrium superconducting states. An attempt is made to take a fresh look at electrodynamics of the MS and try to work out with the issues associated with the description of this most important state of all superconductors. It is shown that the concept of Cooper's pairing along with the Bohr–Sommerfeld quantization condition allows one to construct a semi-classical theoretical model consistently addressing properties of the MS and beyond, including non-equilibrium properties of superconductors caused by the total current. As follows from the model, the three "big zeros" of superconductivity (zero resistance, zero induction and zero entropy) have equal weight and grow from a single root: quantization of the angular momentum of paired electrons. The model predicts some yet unknown effects. If confirmed, they can help in studies of microscopic properties of all superconductors. Preliminary experimental results suggesting the need to revise the standard picture of the MS are presented. [ABSTRACT FROM AUTHOR]

Weakly interacting Fermi liquid can exhibit integer or fractional quantum Hall effect at sufficiently low temperatures, and in the presence of variable applied magnetic and/or electric fields. The said effects have been captured only incompletely by means of the Klitzing conductance formula, e 2 / h multiplied by the dimensionless filling factor (integer or fractional), ν because scattering rate cannot be absent for any conductor that is neither a perfect conductor at zero Kelvin (in the absence of phonons, scattering rate, Cooper pairing and Meissner effect) nor a superconductor. Here, we shall derive the proper microscopic resistance formula based on the notion of Pancharatnam phase retardation that captures both integer and fractional quantum Hall effects. We then compute the Planck constant from the Pancharatnam resistance formula, as well as provide a formal proof for this new formula. We shall unambiguously elaborate why the Pancharatnam resistance formula gives the complete physics of electron transport phenomena responsible for the quantum Hall effects, which include the changes to longitudinal and Hall resistance, as well as the temperature effect. [ABSTRACT FROM AUTHOR]

Microstructural and magnetic characterizations of YBa2Cu3O7−δ nanowire fabric-like samples were performed. Fabric-like ceramic superconductors are nanoporous materials and can be applied, e.g., in magnetic shielding, since the porous morphology makes them extremely light-weight and effectively to be cooled. The samples were produced by the solution blow spinning (SBS) technique, starting from a sol-gel solution of the precursor materials in polyvinyl-alcohol. The morphology of the samples was characterized by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction with the aim to analyze the possible current paths. The magnetic hysteresis loops revealed typical polycrystalline behavior, and field-cooling in various small applied fields shows the presence of the paramagnetic Meissner effect (PME), but in a distinctly different way as compared to melt-texured Bi2Sr2CaCu2O8+δ or Nb. [ABSTRACT FROM AUTHOR]

We report on the magnetic levitation of a millimeter-sized neodymium permanent magnet within the interior of a superconducting radio frequency (SRF) cavity. To the best of our knowledge, this is the first experimental work on levitating a magnet within an SRF cavity. The cavity is a coaxial quarter-wave microwave resonator made from 6061 aluminum, having a resonance frequency of 10 GHz and a loaded Q of 1400. The cylindrical magnet (N50) has a height of 1 mm, a diameter of 0.75 mm, a mass of 4 mg, and a remanence of 1.44 T. This produces a peak magnetic field 140 times greater than the critical field of aluminum. The magnet is placed either on the top of the coaxial portion of the cavity or on the cavity floor before cooling it below the superconducting transition temperature of aluminum. The coaxial mode's resonance frequency shifts as a function of the levitation height of the magnet and gives an idea of the magnet's position and mechanical motion. We observe a transition at a temperature of 650 mK where the Meissner effect levitates the magnet as the material beneath the magnet becomes superconducting. The magnet is levitated to a height of 2.5 mm above the surface of the cavity stub, which is a sufficient separation for the field strength of the magnet at the surface of the stub to be less than the critical field strength of the superconducting aluminum. We measure a 120 MHz upshift in the cavity resonance as the magnet is levitated from the top of the stub and 15 MHz downshift as it levitates from the floor of the cavity. Our measurements are consistent over several heating and cooling cycles. Our work provides a path towards a novel optomechanical system. [ABSTRACT FROM AUTHOR]

Superconductivity is analysed based on the productlike fractal measure approach with fractal dimension a introduced by Li and Ostoja-Starzewski in their attempt to explore anisotropic fractal elastic media. Our study shows the emergence of a massless state at the boundary of the superconductor and the simultaneous occurrence of isothermal and adiabatic processes in the superconductor depending on the position of the electrons. Several physical quantities were found to be position-dependent comparable with those arising in heavy doping and p-n junction. At the boundary of the superconductor, a shrinkage of the magnetic field was observed, leading to a scenario equivalent to the Meissner-Ochsenfeld effect. An enhancement of the London penetration depth is revealed and such an improvement was observed in pnictides at the onset of commensurate spin-density-wave order inside the superconducting phase at zero temperature. The Bardeen-Cooper-Schrieffer theory was also analysed and the appearance of zero-energy states is detected. Nucleation of superconductivity in a bulk was also studied. The system acts as a quantum damped harmonic oscillator and our analysis showed that type-I superconductivity occurs when k < √2/(1 + α), whereas type II occurs for k > √2/(1 + α), where k is the Ginzburg-Landau parameter. The transition at the passage from the 'genuine' to the 'intermediate' type-I estimates 0.767767 <α ≤ 1. [ABSTRACT FROM AUTHOR]