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Several multi‐hydrogen hydrides have exhibited high critical temperature (Tc) superconductivity, but the requirement for ultrahigh pressures limits their applications. Here, high‐throughput calculations are utilized to investigate the superconductivity in few‐hydrogen metal‐bonded (FHMB) perovskites (PVSKs) AHM3 characterized with perfect ambient‐pressure stability. AHM3 is classified into two groups, d and sp superconductors, and provide three indicators that accurately describe AHM3 superconductivity. i) Tc of d superconductors is positively correlated with the number of unpaired d electrons from M atoms; ii) A suitably sized octahedral interstice of H atom is essential for sp superconductors; iii) The introduction of H will further improve the superconductivity, when the M atom has a lower electronegativity than H. ZnHCr3 and ZnHAl3, perfectly meeting the requirements aforementioned, exhibit the highest Tc of 30 and 80 K among the d and sp superconductors, respectively. The results are helpful for understanding the electron–phonon coupling (EPC) mechanism in few‐hydrogen metal‐bonded perovskites and facilitate realizations of ambient‐pressure high‐Tc superconductivity in hydrides. [ABSTRACT FROM AUTHOR]

This article begins with an interdisciplinary review of a hydrodynamic approach to understanding the origins and nature of macroscopic quantum phenomena in high-temperature superconductivity, superfluidity, turbulence and biological systems. Building on this review, we consider new theoretical insights into the origin and nature of pointer states and their role in the emergence of quantum systems. The approach includes a theory of quantum coherence underpinned by turbulence, generated by a field of pointer states, which take the form of recirculating, spin-1/2 vortices (toroids), interconnected via a cascade of spin-1 vortices. Decoherence occurs when the bosonic network connecting pointer states is disrupted, leading to their localisation. Building further on this work, we explore how quantum particles (in the form of different vortex structures) could emerge as the product of a causal dynamic process, within a turbulent (fractal) spacetime. The resulting particle structures offer new insights into intrinsic spin, the probabilistic nature of the wave function and how we might consider pointer states within the standard "point source" representation of a quantum particle, which intuitively requires a more complexed description. [ABSTRACT FROM AUTHOR]

Objective Targeting the inapplicability of conventional train positioning technologies to HTS (high-temperature superconducting) maglev trains, as well as the limitations of existing positioning technologies for such trains, a method based on RFID (radio frequency identification) technology for monitoring train position is proposed. Method The RFID positioning technology is introduced, and a theoretical error model for this technology in system application are proposed. The positioning software and hardware systems are designed and constructed. To improve positioning accuracy of the system, the influence of train operating speed, reader response time, and reader-tag distance on positioning errors are analyzed. On this basis, an experimental platform is established in consideration of the specific operating environment of HTS maglev trains, and the feasibility of the proposed RFID positioning method is verified. Result & Conclusion The designed RFID-based positioning method for HTS maglev trains can achieve relatively high precision positioning of maglev trains running on circular test tracks. The proposed RFID system exhibits advantages such as high reliability, low cost, and easy maintenance.

Abstract FeSe is one of the most enigmatic superconductors. Among the family of iron-based compounds, it has the simplest chemical makeup and structure, and yet it displays superconducting transition temperature ( T c $T_{\text{c}}$ ) spanning 0 to 15 K for thin films, while it is typically 8 K for single crystals. This large variation of T c $T_{\text{c}}$ within one family underscores a key challenge associated with understanding superconductivity in iron chalcogenides. Here, using a dual-beam pulsed laser deposition (PLD) approach, we have fabricated a unique lattice-constant gradient thin film of FeSe which has revealed a clear relationship between the atomic structure and the superconducting transition temperature for the first time. The dual-beam PLD that generates laser fluence gradient inside the plasma plume has resulted in a continuous variation in distribution of edge dislocations within a single film, and a precise correlation between the lattice constant and T c $T_{\text{c}}$ has been observed here, namely, T c ∝ c − c 0 $T_{\text{c}} \propto \sqrt{c- c_{0}}$ , where c is the c-axis lattice constant (and c 0 $c_{0}$ is a constant). This explicit relation in conjunction with a theoretical investigation indicates that it is the shifting of the d xy $d_{\text{xy}}$ orbital of Fe which plays a governing role in the interplay between nematicity and superconductivity in FeSe.

AbstractPhysical measurements of the normal state of an unconventional or high-temperature superconductor in the zero-temperature limit can provide vital information on the nature of the electronic ground state from which the superconductivity emerges. Viable routes to fully suppress the superconductivity include the application of magnetic fields stronger than the upper critical field Hc2 or current densities larger than the critical current density Jc. In high-Tc superconductors, Hc2 is typically higher than the available field strengths, while high currents can often create large heating effects that cause irreparable damage to the sample. Here, we present a technique that combines intense current pulses with high magnetic fields to fully suppress the superconductivity of a candidate high-Tc superconductor while keeping both J and μ0H below their critical values. Two adaptable circuit designs are presented with negligible stray field or self-heating effects (below a critical current value). As a proof of principle, we apply the technique to a high-Tc cuprate with nominal μ0Hc2 ∼ 36 T and demonstrate the suppression of superconductivity down to T/Tc ≤ 0.1 in a field strength of just 24 T. Further applications of this dual technique are also discussed. [ABSTRACT FROM AUTHOR]

For the first time, using tunneling and Andreev spectroscopies of planar break-junctions, we have studied the properties of the superconducting subsystem of K0.8Fe1.7(Se0.72S0.28)2 iron selenide single crystals with a natural phase separation. We have directly determined its energy characteristics: the magnitude of the superconducting order parameter Δ(0), and its characteristic ratio 2Δ(0)/kBTc. The obtained temperature behavior of the critical current Ic(T)/Ic(0) could be fitted with Ambegaokar-Baratoff formula using the experimental 2Δ(0)/kBTc value. [ABSTRACT FROM AUTHOR]

In the 21st century, understanding the mechanism of high-temperature superconductivity has emerged as a pinnacle achievement in condensed matter physics, capturing the lifelong interest of numerous physicists. This paper endeavors to offer a theoretical elucidation for this mechanism, advancing the broader field of physics. Recognizing that high-temperature superconductivity is an aspect of condensed matter physics — underpinned by Maxwell's classical electromagnetic theory — we turn to theoretical mechanics and field theory, which are foundational perspectives in the contemporary scientific era. By framing Maxwell's classical electromagnetic theory within the context of theoretical mechanics and field theory, this paper not only sheds light on the mechanism of high-temperature superconductivity but also recasts Maxwell's theory within a purer theoretical mechanics and field theory domain. This represents a paradigmatic shift and cognitive transformation in physics. Furthermore, leveraging this theoretical mechanics and field theory interpretation of electromagnetic phenomena, we discern that electromagnetic phenomena can be more aptly explained without resorting to the concepts of charges and electric fields, leading to a reinterpretation of Coulomb's law. We propose that protons and electrons might exist as entities devoid of charge-specific attributes and negate the possibility of a strongly correlated particle system within them. [ABSTRACT FROM AUTHOR]

Room-temperature superconductivity has been a long-held dream of mankind and a focus of considerable interest in the research field of superconductivity. Significant progress has recently been achieved in hydrogen-based superconductors found in superhydrides (hydrides with unexpectedly high hydrogen contents) that are stabilized under high-pressure conditions and are not capturable at ambient conditions. Of particular interest is the discovery of a class of best-ever-known superconductors in clathrate metal superhydrides that hold the record for high superconductivity (e.g. T c = 250–260 K for LaH10) among known superconductors and have great promise to be those that realize the long-sought room-temperature superconductivity. In these peculiar clathrate superhydrides, hydrogen forms unusual 'clathrate' cages containing encaged metal atoms, of which such a kind was first reported in a calcium hexa-superhydride (CaH6) showing a measured high T c of 215 K under a pressure of 170 GPa. In this review, we aim to offer an overview of the current status of research progress on the clathrate metal superhydride superconductors, discuss the superconducting mechanism and highlight the key features (e.g. structure motifs, bonding features, electronic structure, etc.) that govern the high-temperature superconductivity. Future research direction along this line to find room-temperature superconductors will be discussed. [ABSTRACT FROM AUTHOR]

Copyright of Urban Mass Transit is the property of Urban Mass Transit Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recently, superconductivity with Tc ≈ 80 K was discovered in La3Ni2O7 under extreme hydrostatic pressure (>14 GPa). For practical applications, we needed to stabilize this state at ambient pressure. It was proposed that this could be accomplished by substituting La with Ba. To put this hypothesis to the test, we used the state-of-the-art atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique to synthesize (La1−xBax)3Ni2O7 films, varying x and the distribution of La (lanthanum) and Ba (barium). Regrettably, none of the compositions we explored could be stabilized epitaxially; the targeted compounds decomposed immediately into a mixture of other phases. So, this path to high-temperature superconductivity in nickelates at ambient pressure does not seem promising. [ABSTRACT FROM AUTHOR]

Wide weaving machines traditionally enhance the weaving width by increasing the shuttle's initial velocity. However, this approach introduces challenges like pronounced equipment vibration, elevated noise levels, heightened energy consumption, and a reduced lifespan. Moreover, its efficacy in significantly widening fabric is constrained. Addressing these concerns, this paper proposes a wide-width warp insertion solution that involves driving the high-temperature superconducting shuttle to achieve high-speed horizontal flight through a traveling magnetic field. The inductive weft insertion system structure of wide weaving machines comprises an insertion guideway with an iron core and wound electromagnetic coils. The shuttle consists of a high-temperature superconducting block and a conductive plate, serving as the driving element. By establishing the equivalent circuit of the weft insertion guideway and the suspended shuttle, the calculation formula for the dynamic driving performance of the weft insertion guideway is obtained. Utilizing a transient 3D magnetic field simulation model, the impact of parameters like the current frequency, shuttle conductive plate thickness, and suspension gap on weft insertion performance is explored. Successful wide-width weft insertion motion is achieved by controlling coil input current parameters. Finally, an experimental platform is constructed to validate the correctness of the weft insertion system structure and simulation model through practical experiments. [ABSTRACT FROM AUTHOR]

We fabricated high-quality c-axis-oriented epitaxial YBa2Cu3O7−x films with 15% of the yttrium atoms replaced by terbium (YTBCO) and studied their electrical properties. The Tb substitution reduced the charge carrier density, resulting in increased resistivity and decreased critical current density compared to pure YBa2Cu3O7−x films. The electrical properties of the YTBCO films showed an in-plane anisotropy in both the superconducting and normal states that, together with the XRD data, provided evidence for, at least, a partially twin-free film. Unexpectedly, the resistive transition of the bridges also demonstrated the in-plane anisotropy that could be explained within the framework of Tinkham's model of resistive transition and the Berezinskii–Kosterlitz–Thouless (BKT) model, depending on the sample parameters. Measurements of the differential resistance in the temperature range of the resistive transition confirmed the occurrence of the BKT transition in the YTBCO bridges. Therefore, we consider the YTBCO films to be a promising platform for both the fabrication of devices with high kinetic inductance and fundamental research on the BKT transition in cuprate superconductors. [ABSTRACT FROM AUTHOR]

The features of materials leading to the strong correlation effect and the phenomena realized in them are considered: the metal-insulator Mott transition and high-temperature superconductivity. The history of their study is traced. Particular attention is paid to studying the role of the interorbital correlation effect and the Hund's coupling in multiorbital systems as well as the electron-phonon interaction in systems with strong Coulomb interaction. The development of the strong coupling diagram technique is analyzed and the results obtained based on the approach used are presented. [ABSTRACT FROM AUTHOR]

Many issues concerning the origin of high-temperature superconductivity (HTS) are still under debate. For example, how the magnetic order varies with doping and its relationship with the superconducting temperature (Tc); and why Tc always peaks near the quantum critical point. In this paper, taking hole-doped La2CuO4 as a classical example, we employ the first-principles band structure and total energy calculations with Monte Carlo simulations to explore how the symmetry-breaking magnetic ground state evolves with hole doping and the origin of a dome-shaped superconductivity region in the phase diagram. We demonstrate that the local antiferromagnetic order and doping play key roles in determining the electron-phonon coupling, thus Tc. Initially, the La2CuO4 possesses a checkerboard local antiferromagnetic ground state. As the hole doping increases, Tc increases with the enhanced electron-phonon coupling strength. But as the doping increases further, the strength of the antiferromagnetic interaction weakens and spin fluctuation increases. At the critical doping level, a magnetic phase transition occurs that reduces the local antiferromagnetism-assisted electron-phonon coupling, thus diminishing the Tc. The superconductivity disappears in the heavily overdoped region when the ferromagnetic order dominates. These observations could account for why cuprates have a dome-shaped superconductivity region in the phase diagram. Our study, thus, contributes to a fundamental understanding of the correlation between doping, local magnetic order, and superconductivity of HTS. [ABSTRACT FROM AUTHOR]

Iron chalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase segregation, where superconducting clusters form at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase segregation. We studied temperature dependences of the photoelectron spectra of Se 3d, Fe 3p, and the valence band at temperatures above and below K of the compound (K Na ) Fe Se with substitution of alkali metal atoms. A strong temperature dependence was found for both the valence band and the core levels: we observed a significant broadening of the spectra, which monotonically decreased with increasing sample temperature under cyclical temperature change. We believe that this broadening is associated with the appearance of volume charges in the dielectric matrix, leading to the band bending. Moreover, the shape of the potential that arises under the surface of this compound was restored, and an estimate was obtained for the relative amount of the superconducting phase. These results will help to better understand the physical processes occurring in this compound. [ABSTRACT FROM AUTHOR]

The behavior of the critical current density is studied in a self-field of a single-crystal NaFe1 –xCoxAs (Tc = 21.1 K) sample in the temperature range from 4 K to Tc. Within the Bardeen–Cooper–Schrieffer (BCS) model, the dependences of the superconducting carrier density ρs(T) are obtained under the assumption of the two-band case. It is shown in the case of two-gap uperconductivity, the experimental data are well described by the theory, and the superconducting gaps Δ(0) obtained by approximation are in agreement with the values determined by studying the Andreev reflection spectra. [ABSTRACT FROM AUTHOR]

Copyright of e & i Elektrotechnik und Informationstechnik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using incoherent multiple Andreev reflection effect spectroscopy, the gap structure of superconducting (the 122-Se family) and the temperature evolution of the features caused by Andreev transport in I(V) and dI(V)/dV curves of planar SnS-contacts formed in this compound: the Andreev excess current at and the Andreev zero-bias conductance are studied for the first time. The magnitude of the superconducting order parameter meV is determined. The possibility of describing the obtained results within the available theoretical models is discussed. [ABSTRACT FROM AUTHOR]

This article begins with an interdisciplinary review of a hydrodynamic approach to understanding the origins and nature of macroscopic quantum phenomena in high-temperature superconductivity, superfluidity, turbulence and biological systems. Building on this review, we consider new theoretical insights into the origin and nature of pointer states and their role in the emergence of quantum systems. The approach includes a theory of quantum coherence underpinned by turbulence, generated by a field of pointer states, which take the form of recirculating, spin-1/2 vortices (toroids), interconnected via a cascade of spin-1 vortices. Decoherence occurs when the bosonic network connecting pointer states is disrupted, leading to their localisation. Building further on this work, we explore how quantum particles (in the form of different vortex structures) could emerge as the product of a causal dynamic process, within a turbulent (fractal) spacetime. The resulting particle structures offer new insights into intrinsic spin, the probabilistic nature of the wave function and how we might consider pointer states within the standard “point source” representation of a quantum particle, which intuitively requires a more complexed description.

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Today, high-temperature superconducting (HTS) current limiters and transformers allow to limit the surge short circuit current during failure without negatively affecting on the power grid com-plex at the normal operation mode. However, the transition of a superconductor to a resistive state at the moment of current limitation can cause significant heat generation, which can destroy the transformer windings. The research goal is to provide optimal technical characteristics of the HTS transformer to achieve effective short circuit current limitation and prevent thermal breakdown of its windings. To achieve this goal, a mathematical model of a HTS transformer was developed. The presented method considers the material type and geometry of the superconducting tape, the critical parameters of the superconductor (current and temperature), the parameters of the cryogenic liquid, dependence of the resistance and heat capacity of the HTS tape layers on temperature. The simulation model was created in the Matlab/Simulink software. The most important result is the possibility of obtaining optimal elec-trical and thermal parameters of the HTS transformer windings during the short circuit current limitation, as well as ensuring the thermal stability of the superconducting tape at the quench moment. The obtained results are significant in the design and operation of HTS transformers. For efficient and safe operation in the current-limiting mode, it is necessary to take into account heat generation on the transformer windings. It is important for the superconductor returning to the superconducting state without causing significant overheating of the windings.

Recently, superconductivity with Tc ≈ 80 K was discovered in La3Ni2O7 under extreme hydrostatic pressure (>14 GPa). For practical applications, we needed to stabilize this state at ambient pressure. It was proposed that this could be accomplished by substituting La with Ba. To put this hypothesis to the test, we used the state-of-the-art atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique to synthesize (La1−xBax)3Ni2O7 films, varying x and the distribution of La (lanthanum) and Ba (barium). Regrettably, none of the compositions we explored could be stabilized epitaxially; the targeted compounds decomposed immediately into a mixture of other phases. So, this path to high-temperature superconductivity in nickelates at ambient pressure does not seem promising.

Wide weaving machines traditionally enhance the weaving width by increasing the shuttle’s initial velocity. However, this approach introduces challenges like pronounced equipment vibration, elevated noise levels, heightened energy consumption, and a reduced lifespan. Moreover, its efficacy in significantly widening fabric is constrained. Addressing these concerns, this paper proposes a wide-width warp insertion solution that involves driving the high-temperature superconducting shuttle to achieve high-speed horizontal flight through a traveling magnetic field. The inductive weft insertion system structure of wide weaving machines comprises an insertion guideway with an iron core and wound electromagnetic coils. The shuttle consists of a high-temperature superconducting block and a conductive plate, serving as the driving element. By establishing the equivalent circuit of the weft insertion guideway and the suspended shuttle, the calculation formula for the dynamic driving performance of the weft insertion guideway is obtained. Utilizing a transient 3D magnetic field simulation model, the impact of parameters like the current frequency, shuttle conductive plate thickness, and suspension gap on weft insertion performance is explored. Successful wide-width weft insertion motion is achieved by controlling coil input current parameters. Finally, an experimental platform is constructed to validate the correctness of the weft insertion system structure and simulation model through practical experiments.

The current study presents the results of tunneling spectroscopy measurements of current-voltage characteristics (CVC) and dynamic conductance spectra of SnS tunneling contacts in single crystals of slightly overdoped superconducting ferro-pnictide of nominal composition BaFe Ni As with bulk critical temperature K. Besides the Andreev structure, a strong nonlinearity is observed in the obtained curves both in the superconducting and normal state. The positions and temperature dependences of the observed -features unrelated to the superconducting state are determined for the temperature range K. The paper analyzes possible reasons for the emergence of the observed features. [ABSTRACT FROM AUTHOR]

A method for searching and synthesizing new HTSC with higher critical temperatures (Tc) is proposed. It is assumed that an increase in Tc in cuprate superconductors requires not only to increase the number of CuO2 planes in superconducting layers, but also to add fluorine anions to Ca or Y planes. Possible crystal structures and chemical formulas of compounds with higher critical temperatures are proposed. [ABSTRACT FROM AUTHOR]

This paper describes a universal method proposed by the author for the evaluative analytical calculation of the main parameters of synchronous electrical machines, including superconducting ones. Traditional methods for analytical calculation of parameters to build a phasor diagram of electrical machines require a calculation of all dimensions of the active zone, tooth-slot zone and frontal parts of armature windings. All sizes and local states of magnetic circuit saturation are necessary for the calculation of magnetic conductivities. Traditional analytical methods use, among other things, empirical formulas and non-physical coefficients and allow one to calculate only standard machines with classic tooth-slot zones and armature winding types. As a result of drawing a phasor diagram using traditional methods, the angle between the electromotive force and voltage is calculated, which is the machine's internal parameter and has no major significance for users. The application of modern computer programs for simulation requires a preliminary analytical calculation in order to obtain all dimensions of the three-dimensional model. FEM simulation programs are expensive, require expensive high-performance computers and highly paid skilled personnel. Fast analytical techniques are also required to assess the correctness of the obtained automatic computer simulation results. The proposed analytical method makes it possible to quickly obtain all the main parameters of a newly designed machine (including superconducting ones and those of non-traditional design) without a detailed calculation of the dimensions of the tooth-slot zone and armature end-windings. The characteristic values of load angles are set according to the results of simple calculations, and the desired values, obtained via plotting, represent the inductive resistances of armature winding and inductive voltage drop across it. Results of practical significance, calculated from the voltage diagram, are as follows: the inductor's magnetomotive force necessary to maintain the nominal load voltage value, regardless of the magnitude (including double overload) and type of the connected load, or the main dimensions of the active zone. [ABSTRACT FROM AUTHOR]

Charge order has recently been identified as a leading competitor of high-temperature superconductivity in moderately doped cuprates. We provide a survey of universal and materials-specific aspects of this phenomenon, with emphasis on results obtained by scattering methods. In particular, we discuss the structure, periodicity, and stability range of the charge-ordered state, its response to various external perturbations, the influence of disorder, the coexistence and competition with superconductivity, as well as collective charge dynamics. In the context of this journal issue which honors Roger Cowley's legacy, we also discuss the connection of charge ordering with lattice vibrations and the central-peak phenomenon. We end the review with an outlook on research opportunities offered by new synthesis methods and experimental platforms, including cuprate thin films and superlattices.

Charge order has recently been identified as a leading competitor of high-temperature superconductivity in moderately doped cuprates. We provide a survey of universal and materials-specific aspects of this phenomenon, with emphasis on results obtained by scattering methods. In particular, we discuss the structure, periodicity, and stability range of the charge-ordered state, its response to various external perturbations, the influence of disorder, the coexistence and competition with superconductivity, as well as collective charge dynamics. In the context of this journal issue which honors Roger Cowley's legacy, we also discuss the connection of charge ordering with lattice vibrations and the central-peak phenomenon. We end the review with an outlook on research opportunities offered by new synthesis methods and experimental platforms, including cuprate thin films and superlattices.

As a new type of magnetic levitation train with the characteristics of self-stabilization and self-suspension, high-temperature superconducting magnetic levitation has developed to the test line research stage. In order to promote the rapid development of high-temperature superconducting magnetic levitation train engineering, and the main electromagnetic radiation sources are clarified by analyzing their working principles and structures. Then Ansoft Maxwell EM was used to build a 3D magnetic levitation train electromagnetic environment simulation model to simulate and predict the electromagnetic radiation characteristics of the magnetic levitation train system. Finally, a field EMF test was carried out to verify and assess the impact on the EM environment in the system. The results show that the permanent magnet track on the ground and the synchronous linear motor are the primary electromagnetic radiation sources, and the generated fields are mainly low-frequency fields and static magnetic fields. The low-frequency magnetic field inside the train decreases with the increase of frequency and is partially shielded by the carriage; The static magnetic field cannot be weakened by the carriage, and the static magnetic field inside the car decreases with the increase of height. All types of electromagnetic fields are far below the requirements of the relevant electromagnetic environmental standard limits, and have no effect on the electromagnetic radiation safety of the personnel inside the train and the surrounding environment; In considering of the special people who have pacemakers, static magnetic field suppression measures are studied, and the results show that the trains with high magnetic permeability permalloy as the shielding layer at the bottom of the vehicle greatly lower the static magnetic field within the train. [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]

It is demonstrated, that recently proposed by the author Q-ball mechanism of the pseudogap state and high-Tc superconductivity in cuprates may be detected in micro X-ray diffraction, since it imposes inverse correlations between the size and scattering intensities of the Q-ball charge-density-wave (CDW) fluctuations in these compounds. The Q-ball charge Q gives the number of condensed elementary bosonic excitations in a CDW fluctuation of finite amplitude. The attraction between these excitations inside Euclidean Q-balls is self-consistently triggered by the simultaneous condensation of Cooper/local pairs. Euclidean Q-ball solutions, analogous to the famous Q-balls of squarks in the supersymmetric standard model, arise due to the global invariance of the effective theory under the U (1) phase rotation of the Fourier amplitudes of the short-range CDW fluctuations. A conserved 'Noether charge' Q along the Matsubara time axis equals Q ∝ T M 2 V , where the temperature T, Q-ball's volume V, and fluctuation amplitude M enter. Several predictions are derived in an analytic form that follow from this picture. The conservation of the charge Q leads to an inverse proportionality between the volume V and X-ray scattering intensity ∼ M 2 of the CDW puddles found in micro X-ray scattering experiments. The theoretical temperature dependences of the most probable Q value of superconducting Q-balls and their size and scattering amplitudes fit well the recent X-ray diffraction data in the pseudogap phase of high-Tc cuprates. [ABSTRACT FROM AUTHOR]

We fabricated high-quality c-axis-oriented epitaxial YBa2Cu3O7−x films with 15% of the yttrium atoms replaced by terbium (YTBCO) and studied their electrical properties. The Tb substitution reduced the charge carrier density, resulting in increased resistivity and decreased critical current density compared to pure YBa2Cu3O7−x films. The electrical properties of the YTBCO films showed an in-plane anisotropy in both the superconducting and normal states that, together with the XRD data, provided evidence for, at least, a partially twin-free film. Unexpectedly, the resistive transition of the bridges also demonstrated the in-plane anisotropy that could be explained within the framework of Tinkham’s model of resistive transition and the Berezinskii–Kosterlitz–Thouless (BKT) model, depending on the sample parameters. Measurements of the differential resistance in the temperature range of the resistive transition confirmed the occurrence of the BKT transition in the YTBCO bridges. Therefore, we consider the YTBCO films to be a promising platform for both the fabrication of devices with high kinetic inductance and fundamental research on the BKT transition in cuprate superconductors.

Hydrogen‐rich materials synthesized at megabar pressures have revolutionized the field of high‐temperature superconductivity. Among hydrogen‐rich materials, clathrate hydrides which show near‐room‐temperature superconductivity have been discovered in recent years. Herein, clathrate actinide hydrides are constructed, and their electronic properties and electron–phonon interaction as well as superconductivity under high pressures are theoretically investigated with density functional theory tools. The calculations adopt projected‐augmented‐wave (PAW) approach. The Perdew–Burke–Ernzerhof (PBE)‐type generalized gradient approximation (GGA) is used for the exchange–correlation potentials. Specifically, Th–H and Pu–H compounds are presented, of which the stability is demonstrated via calculated phonon dispersions, and the superconducting transition temperatures Tc under 100, 200, and 400 GPa are estimated. ThH10 among Th–H compounds has the highest transition temperature of superconductivity, and Tc of ThH10 can reach 151.8 K under 200 GPa. PuH10 is also better than other investigated Pu–H compounds in superconductivity, but the highest Tc of PuH10 is only 31.4 K under 400 GPa, much lower than that of ThH10. [ABSTRACT FROM AUTHOR]

The discovery of high-temperature superconductivity (HTS) was a momentous event. This article explores the social and institutional history of HTS research in China between 1987 and 2008. Desire for a Nobel Prize shaped the Chinese state's initial push to establish the National Superconductivity Research Program. Yet, after the enthusiasm for HTS research cooled, and even after a Nobel Prize for HTS was awarded to non-Chinese scientists, financial and institutional support for the research continued. This process fostered the 'to live' ethos of science, which has replaced the Nobel Prize dream as a central mechanism of interaction between the state and science in China. Indeed, Chinese HTS research not only survived, but also produced an abundance of 'normal science' discoveries. This pattern continued after 2008, when Japanese scientists made the groundbreaking innovation of iron-based superconductivity and Chinese scientists quickly turned their attention to this sub-field. They published many papers pushing the field forward slightly, rather than making the largest scientific advances. The mutual interaction between the state and scientists underpinned this phenomenon: On the one hand, the productivity of normal science has helped to maintain state legitimacy. On the other hand, the evaluation and incentive systems, as well as deep-rooted cultural features such as officialism, utilitarianism, and the foregrounding of politics lead scientists to opportunistically pursue normal science. The state and scientists have co-produced a regime of normal science. [ABSTRACT FROM AUTHOR]

A complex deposition process of high-temperature superconducting (HTS) thin films and coated conductors is usually optimized by concentrating on the crystalline quality of the material, thus getting the best possible critical temperature and self-field properties. However, most of the HTS power applications that are based on coated conductors act at high magnetic fields, and thus an alternative approach focusing on the formation of an optimal network of columnar flux pinning centers is more reasonable. Therefore, we systematically show how a lengthening of the deposition distance produces perfectly aligned and distinctly longer self-assembled BaZrO3 (BZO) nanorods within the YBa2Cu3O6+x (YBCO) matrix. This method unambiguously enhances in-field properties such as pinning force, critical current density, and its isotropy along the YBCO c axis. The experimental results, especially formation of the c peak where the relative length of the nanorod is a key issue, are confirmed by the vortex dynamics simulations. Finally, we present a semiquantitative model governing the formation of nanorods that explains the experimentally observed improved nanorod growth as a function of the deposition distance via the associated variation of the fractional partial pressure between atomic species within the laser plume. [ABSTRACT FROM AUTHOR]

Novel nanoscale probes are opening new venues for understanding unconventional electronic and magnetic functionalities driven by multiscale lattice complexity in doped high-temperature superconducting perovskites. In this work, we focus on the multiscale texture at supramolecular level of oxygen interstitial (O-i) atomic stripes in HgBa2CuO4+y at optimal doping for the highest superconducting critical temperature (TC) of 94 K. We report compelling evidence for the nematic phase of oxygen interstitial O-i atomic wires with fractal-like spatial distribution over multiple scales using scanning micro- and nano-X-ray diffraction. The scale-free distribution of O-i atomic wires at optimum doping extending from the micron down to the nanoscale has been associated with the intricate filamentary network of hole-rich metallic wires in the CuO2 plane. The observed critical opalescence provides evidence for the proximity to a critical point that controls the emergence of high-temperature superconductivity at optimum doping. [ABSTRACT FROM AUTHOR]

Impedance matching and heat management are important factors influencing the performance of terahertz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered containing either a conventional large single crystal or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes play important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts terahertz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based, devices. These results are in good agreement with presented experimental data.

Harnessing the fascinating properties of correlated oxides requires precise control of their carrier density. Compared to other methods, oxygen doping provides an effective and more direct way to tune the electronic properties of correlated oxides. Although several approaches, such as thermal annealing and oxygen migration, have been introduced to change the oxygen content, a continuous and reversible solution that can be integrated with modern electronic technology is much in demand. Here, we report a novel ionic field-effect transistor using solid Gd-doped CeO2 as the gate dielectric, which shows a remarkable carrier-density-tuning ability via electric-field-controlled oxygen concentration at room temperature. In Bi2Sr2CaCu2O8+δ (Bi-2212) thin flakes, we achieve a reversible superconductor–insulator transition by driving oxygen ions in and out of the samples with electric fields, and map out the phase diagram all the way from the insulating regime to the over-doped superconducting regime by continuously changing the oxygen doping level. Scaling analysis indicates that the reversible superconductor–insulator transition for the Bi-2212 thin flakes follows the theoretical description of a two-dimensional quantum phase transition. Our work provides a route for realizing electric-field control of phase transition in correlated oxides. Moreover, the configuration of this type of transistor makes heterostructure/interface engineering possible, thus having the potential to serve as the next-generation all-solid-state field-effect transistor. [ABSTRACT FROM AUTHOR]

The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity ρ(T) of an optimally doped YBa2Cu3O7−δ single crystal has been studied. The temperature dependences of both fluctuation conductivity σ′ (T) and the pseudogap Δ*(T) on irradiation dose φ have been calculated within the local pair model. Here we show that with an increase in φ, the value of ρ(300 K) increases linearly, while Tc decreases linearly. Concurrently, the value of ρ(100 K) increases nonlinearly, demonstrating a feature for φ3 = 4.3⋅1018 e/cm2, which is also observed in the number of other dose-dependent parameters. Regardless of the irradiation dose, in the temperature range from Tc up to T01, σ′(T) obeys the classical fluctuation theories of Aslamazov-Larkin (3D-AL) and Maki-Thompson (2D-MT), demonstrating 3D-2D crossover with increasing temperature. The crossover temperature T0 makes it possible to determine the coherence length along the c axis, ξc(0), which increases by ∼3 times under irradiation. Furthermore, the range of superconducting fluctuations above Tc also noticeably increases. At φ1 = 0, the dependence Δ*(T) typical for single crystals containing pronounced twin boundaries is observed with a maximum at Tpair ∼120 K and a distinct minimum at T = T01. It was determined for the first time that at φ3 = 4.3⋅1018 e/cm2 the shape of Δ*(T) changes strongly and becomes the same as in optimally doped YBa2Cu3O7−δ single crystals with a very low pseudogap opening temperature T* and noticeably reduced Tpair, while at Tc(φ) there are no singularities. With an increase in the irradiation dose up to φ4 = 8.81018 e/cm2, the shape of Δ*(T) is restored and becomes the same as in well-structured YBa2Cu3O7−δ films and untwined single crystals. Moreover, in this case, Tpair and T* increase noticeably. [ABSTRACT FROM AUTHOR]