High-temperature Superconductors Research Articles

Compressed Sr superconducting transition temperature up to 17.65 K.

Due to the simplicity of their composition, the study of the superconducting properties of elemental substances holds significant importance for understanding the mechanisms of high-temperature superconductivity. This work involves simulated calculations to investigate the phase transition sequence and superconducting properties of Sr under pressure. The stability range of the Sr-IV phase C2/c was redefined, determining that it can extend up to 150 GPa, and the phase transition sequence of Sr under high pressure was studied. It was discovered that the d-electrons in the Sr-IV phase significantly contribute to the Fermi surface, a phenomenon closely related to the Van Hove singularity (VHS) near the saddle points. The increase in Tc of Sr under pressure is attributed to phonon softening and strong coupling resulting from the gradual overlap of VHS with the Fermi level, which is associated with the incomplete saturation of s-d electron transfer. Ultimately, the Tc of Sr reaches 17.65 K at 150 GPa, with a λ value of 1.26. This strong EPC is contributed by the interaction between d-electrons and medium-high-frequency phonons. This study extends new pathways for investigating the superconductivity of high-pressure phases of Sr and provides new insights for the theoretical study of elemental superconductors.

Prospect of high-temperature superconductivity in layered metal borocarbides

A large-scale ab initio search for conventional superconductors has revealed new thermodynamically stable and metastable layered metal borocarbides expected to form under ambient pressure and display critical temperatures exceeding 70 K.

Orientated hydrogen chains favor superconductivity in germanium sulfur hydrides

Hydrogen-rich compounds, as the closest to room-temperature superconductors discovered in recent years, have attracted the research interest of scientists. Especially the recent theory-orientated discovery of record high-temperature superconductivity (Tc∼330 K)...

The effect of the modelling approaches in the assessment of comfort and curve negotiation performance of a small-scale maglev vehicle

In this article, a new co-simulation method was presented for high-temperature superconducting (HTS) magnetic levitation (Maglev) systems by utilizing H-formulation that is implemented in COMSOL Multiphysics®. A comparative study was conducted to evaluate the curve negotiation performance, which is closely related to its stability, of the HTS maglev vehicle running on a multi-surface permanent magnet guideway (PMG). Also, Sperling’s ride index method was used to evaluate ride comfort. Different from the existing related models of this subject, the dynamics of free-falling were incorporated into the modelling approach to simulate the actual running conditions of the vehicle. In addition, because of considering the non-stationary dynamics of the induced supercurrent in the HTS domain, the proposed approach and the selected route design provide simulation results that are close to the actual application of the HTS maglev vehicle. The results show that the performance indicators of the co-simulation greatly deviate from those of the existing curve-fitting-based models with increasing velocity.

Overall design of a 5 MW/10 MJ hybrid high-temperature superconducting energy storage magnets cooled by liquid hydrogen

The integration of superconducting magnetic energy storage (SMES) into the power grid can achieve the goal of storing energy, improving energy quality, improving energy utilization, and enhancing system stability. The early SMES used low-temperature superconducting magnets cooled by liquid helium immersion, and the complex low-temperature cooling system greatly limited the promotion and application of such devices. SMES based on high temperature superconductivity (HTS) materials can operate in the temperature range of 15–30 K, which simplifies the cooling system and reduces the cooling loss, and greatly improves the operating efficiency and stability of the cooling system. In this paper, the overall design of a 5 MW/10 MJ SMES based on state of the art HTS materials is achieved. The structural parameters of YBCO and MgB2 cables are introduced and the structural parameters of energy storage magnet are analyzed. And the cooling scheme for SMES is provided.

High-temperature superconductivity mechanism and an alternative theoretical model of Maxwell’s classical electromagnetism theory

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.

Enhanced critical current density in optimized high-temperature superconducting bilayer thin films

The superconducting and structural properties of bilayer thin films based on YBa2Cu3O 7−x / YBa2Cu3O 7−x +6%BaZrO3 heterstructures have been studied. In a broad range of magnetic field strengths and temperatures, the optimal bilayer film comprises 30% YBCO at the substrate interface and 70% YBCO+6%BZO on the top. The critical current density measured for the optimal bilayer structure is shown to outperform the corresponding single layer films up to almost 60%. The obtained results are comprehensively discussed in the light of our previously published theoretical framework (Rivasto et al 2023 J. Phys.: Condens. Matter 35 075701:1–10). We conclude that the bilayering provides an efficient and easily applicable way to further increase the performance and applicability of high-temperature superconductors in various applications. Consequently, the bilayer films should be seriously considered as candidates for the upcoming generation of coated conductors.

Designing the stripe-ordered cuprate phase diagram through uniaxial-stress.

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La[Formula: see text]Ba[Formula: see text]CuO[Formula: see text], with [Formula: see text] = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO[Formula: see text] plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature [Formula: see text] and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of [Formula: see text]0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal [Formula: see text]. Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism.

Critical current of a layered high-temperature superconductor with artificial pinning centers: the Monte Carlo simulation

Current–voltage characteristics (EJ curves) and magnetic field dependences of the critical current have been calculated for a superconductor with artificial pinning in the form of submicron-sized holes and tilted radiation defects. Calculations have been performed within the framework of the three-dimensional model of a layered HTS by means of the Monte Carlo method. S-shaped features of the EJ curves have been observed for a sample with a rectangular lattice of holes. Such features have not occurred in calculations for HTSs with non-magnetic pinning centers before, but they have been observed in experimental studies. In this paper, the features occurred in magnetic fields close to 290 Gs (which is the lower critical field for the Bi2Sr2CaCu2O8-δ superconductor at 1 K) and they were sensitive to the magnitude of the external magnetic field. In addition, the features were more prominent at temperatures below 30 K and in samples with weak intrinsic pinning, and they were connected with matching-like effects in the vortex system (i. e. a certain number of vortices being pinned on each hole, screening new vortices from entering the sample). For samples with tilted radiation defects, decreasing field dependences of the critical current have been obtained, showing weak maxima near the lower critical field of the superconductor. Calculations have shown that, at a fixed value of the external field, the critical current decreases with the increasing tilt angle of the defects.

Optimization Study of Cooling Channel for the Oil Cooling Air Gap Armature in a High-Temperature Superconducting Motor

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

Development of the sorption-integrated adiabatic demagnetization refrigerator (ADR) without active heat switches

This study reports on the test results of a proof of concept sorption-integrated adiabatic demagnetization refrigerator (ADR) for sub-Kelvin cooling. The configuration of the cooler is primarily simplified by eliminating heat switches which require active control. The whole refrigerator apparatus is composed of the high temperature superconducting (HTS) magnet to magnetize the single crystal Gadolinium Gallium Garnet (GGG), and the 4He sorption cooler. Both the sorption cooler and the magnet are cooled by a 4 K two-stage Gifford-McMahon (G–M) cooler. The sorption cooler consists of a sorption pump filled with activated carbon of 13.9 g and a gravitiy-assisted-4He thermosiphon with volume of 5.0 cm3. The pressure inside the thermosiphon is controlled by changing the adsorption capacity of the sorption pump. The performance of the developed cooler is preliminarily evaluated by a single-shot test. The sorption cooler precools the 3 T-magnetized GGG from 4.40 K to 1.94 K by evaporating the liquid helium contained in the thermosiphon. When helium inside the thermosiphon is evacuated by the sorption pump, the magnetized GGG is thermally disconnected from the 4 K heat sink. Subsequently, the GGG is adiabatically demagnetized by discharging the HTS magnet and reaches temperature of 0.55 K. However, after demagnetization, the gas helium inside the cooling system is condensed by the GGG, consequently reducing its cooling capacity. Detailed experimental results are presented and discussed in the remainder of the paper.

Enhancement of high-temperature superconducting coil stability using doped smart insulation materials for superconducting magnet applications

This study reports a high-temperature superconducting (HTS) coil containing molybdenum doped vanadium trioxide (V2O3:Mo) as turn-to-turn insulation material to ameliorate the electrical properties of both insulated and non-insulated (NI) coils. The electrical characteristics and thermal stability of the V2O3:Mo insulated coil against NI and V2O3 insulated coils were investigated through charge-discharge, over-current, and quench tests. The findings revealed that the V2O3:Mo and V2O3 insulated coils demonstrated a faster charge/discharge rate than the NI coil due to the high resistance of the V2O3: Mo or V2O3 insulator which obstructed the current to flow away from the azimuthal current path. In the over-current test at 160A, the V2O3:Mo insulated and NI coils exhibited higher electrical stability than the V2O3 insulated coil because the excessive currents above their critical values bypassed between the turn-to-turn contact. Moreover, the V2O3:Mo insulated coil demonstrated a 2.1times improvement in the minimum quench energy compared to the V2O3 insulated coil at 70 % of the coil's current-carrying capacity, which is an essential performance parameter for the operation of superconducting magnets.

Interaction of in-plane Drude carrier with c-axis phonon in PdCoO2

We performed polarized reflection and transmission measurements on the layered conducting oxide PdCoO2 thin films. For the ab-plane, an optical peak near Ω ≈ 750 cm−1 drives the scattering rate 1/τ(ω) and effective mass m*(ω) of the Drude carrier to increase and decrease respectively for ω ≧ Ω. For the c-axis, a longitudinal optical phonon (LO) is present at Ω as evidenced by a peak in the loss function Im[−1/εc(ω)]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at Ω results from an electron-phonon coupling of the ab-plane carrier with the c-LO phonon, which leads to the frequency-dependent 1/τ(ω) and m*(ω). This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared (IR) band and a c-LO. On the contrary, it is the Drude carrier that couples in PdCoO2. The coupling between the ab-plane Drude carrier and c-LO suggests that the c-LO phonon may play a significant role in the characteristic ab-plane electronic properties of PdCoO2, including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.

Detection of Radiation Generated by Moving Josephson Vortices in a Bi<sub>2 +</sub> <sub><em>x</em></sub>Sr<sub>2 –</sub> <sub><em>x</em></sub>CuO<sub>6 + δ</sub> Single Crystal in High Magnetic Fields Directly in the Sample

A high-temperature superconductor sample with numerous internal Josephson junctions formed by atomic layers is a nonlinear system with unique dynamic properties. An external magnetic field penetrates in the sample in the form of moving Josephson vortices, which generate radiation. It has been shown that this radiation in a Bi2 +xSr2 –xCuO6 + δ(Bi2201) single crystal can be detected by means of a Josephson junction on a microbreak (break junction) directly inside the single crystal.

A flux pump driven non-soldering closed-loop HTS magnet and its electromagnetic-thermal semi-analytical modelling method

We propose a new flux pump driven non-soldering closed-loop (NSCL) high temperature superconducting (HTS) magnet free of any soldering joints throughout the magnet for persistent current mode (PCM) operation. All the superconducting parts of the magnet are wound directly with HTS closed-loop ring split from an 8 mm REBCO tape using our new cutting scheme free of any soldering requirements. The magnet contains two single-pancake coils connected in series forming a closed circuit through two parallel bridge branches. Two thermal switches set on the two bridge branches control the on–off of the two bridges. A copper coil with iron core installed around one of the bridges is employed as the flux pump to drive the HTS magnet. An electromagnetic-thermal semi-analytical modelling method is proposed to analyse the pumping process by which the transport current in the magnet is calculated. The theoretical limit equation of the saturation current is improved as well. The proposed method can predict the current of the NSCL HTS magnet during the pumping process and provide results that are close to experiments. Experiments verify both the feasibility of the proposed flux pump driven NSCL HTS magnet and the modelling method. The results show that the NSCL HTS magnet works well in the PCM, which provides inspiration to the design of PCM operation of high field HTS magnets. The proposed modelling method also helps guide the design of different forms of HTS magnets and the flux pumps driving them.

Elastoplastic mechanical behavior of high-field magnet of REBCO high temperature superconducting composite tape under extreme environment

Rare Earth-Barium-Copper-Oxide (REBCO) high temperature superconducting (HTS) coated conductors (CCs) are one of the best candidate materials for high-field magnets. However, due to its laminated structure, each component materials of the CCs are inevitably subjected to residual thermal stress and electromagnetic force during heat treatment, processing, cooling, coil winding, and operation of the magnet structure. It causes changes in its superconducting properties, and even leads to irreversible degradation of superconducting critical characteristics, brittle layer fracture and peeling delamination within the coil. To reveal the synthesis of the tape and the stress state of the high-field coil under multi-physical fields. The residual thermal stress/strain accumulation of each component material of the tape is investigated under two thermal processing and manufacturing methods by combining analytical theory with numerical calculation. In which, the two thermal processing methods are metal-organic chemical vapor deposition (MOCVD) process and one-step cooling simplified process respectively. The results show that the residual thermal stresses accumulated by five materials, Hastelloy, Buffer, REBCO, Ag and Cu, under the step-by-step synthesis process are about 14.7%, 97.3%, 96.3%, 80% and 49.2% of the simplified model, respectively. And the residual thermal strains are about 15.1%, 96.8%, 95.2%, 85.2% and 27.5% of the simplified model. In addition, after the five materials are manufactured according to the step-by-step thermal processing process, the accumulated residual thermal stresses are about 1.88%, 86.3%, 61%, 114.3%, and 34% of their respective yield strengths, respectively. The elastoplastic mechanical behavior of the magnet under the background of high magnetic field and strong current is also studied. The results indicate that the maximum values of effective and hoop stresses in each component material of the coil are distributed in the innermost side of the magnet, and decrease gradually along the radial direction of the magnet. In the innermost coil of the magnet, the effective stress of each component material increases with the increase of the transmission current. When the transmission current Iope = 183 A, the material Cu reaches the yield strength and enters the plastic deformation stage. Whereas the material Hastelloy reaches the yield strength and enters into the plastic deformation stage when the transmission current Iope = 222 A.

Optimization of heating profile for superconductor joint performance made by resistive joule heating process

The long-term heating (>60 min) of second generation high temperature superconductor (2G HTS) tape-joints at temperatures above 200 °C leads to the continuous deterioration of their superconducting properties. Previously, we proposed a resistive Joule heating process with a short heating time (∼10 min) that exhibited beneficial critical current (Ic), retention percentages (84–99 %), and joint resistances (74–697 nΩ cm2) in four independent experiments.In this study, we investigated two heating rates and three tape-joint areas. The results show that for the samples with different tape joint areas, the critical current retention percentages (97–100 %) and uniformity of specific joint resistances (82–272 nΩ cm2) were significantly improved at a high heating rate of ∼30 °C/min. The sintering of silver nanoparticles and oxidation characteristics of the copper stabilizers were observed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy to elucidate the effect of different heating profiles. This study opens new avenues for improving the quality of 2G HTS tape joint processes for ultrahigh magnetic field applications.

Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors.

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd2-xCexCuO4-δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm2. The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions.

Signature of Superconductivity in Pressurized La4Ni3O10

The discovery of high-temperature superconductivity near 80 K in bilayer nickelate La3Ni2O7 under high pressures has renewed the exploration of superconducting nickelate in bulk materials. The extension of superconductivity in other nickelates in a broader family is also essential. Here, we report the experimental observation of superconducting signature in trilayer nickelate La4Ni3O10 under high pressures. By using a modified sol-gel method and post-annealing treatment under high oxygen pressure, we successfully obtained polycrystalline La4Ni3O10 samples with different transport behaviors at ambient pressure. Then we performed high-pressure electrical resistance measurements on these samples in a diamond-anvil-cell apparatus. Surprisingly, the signature of possible superconducting transition with a maximum transition temperature (T c) of about 20 K under high pressures is observed, as evidenced by a clear drop of resistance and the suppression of resistance drops under magnetic fields. Although the resistance drop is sample-dependent and relatively small, it appears in all of our measured samples. We argue that the observed superconducting signal is most likely to originate from the main phase of La4Ni3O10. Our findings will motivate the exploration of superconductivity in a broader family of nickelates and shed light on the understanding of the underlying mechanisms of high-T c superconductivity in nickelates.

Levitation force measurement and characteristics analysis of double sided high temperature superconducting thin film device

In this paper, the levitation characteristics of double sided high temperature superconducting (HTS) thin film device is proposed and measured. Based on the unique advantages such as, passive self-stable levitation, higher payload, lower energy consumption, less maintenance cost, etc., HTS-magnetic levitation (maglev) technology has been applied in the traditional fields (rail transit and energy storage fields) and novel fields (astrophysics, space station microgravity, vibration isolation fields). As the key core components, HTS device should meet the requirements of volume, weight and cost, to improve the system operation efficiency. Thus, considering the low profile, miniaturization and lightweight characteristics of the double sided YBa2Cu3O7-x (YBCO) thin film, we measured its levitation and relaxation characteristics. Meanwhile, we also designed the YBCO thin film with meander-lines, to explore the levitation characteristic evolution mechanism. It can be found from the experimental results that, the single piece of YBCO thin film with/without meander-lines can offer the levitation force more than 400 mN and 800 mN, respectively. The signature of this work is that the double sided YBCO thin film has the potential to be employed as the core device in the special application fields (such as astrophysics and space station), to supply the sufficient micro levitation force in limited volume and weight.