High-temperature Superconductors Research Articles

Navigation of superparamagnetic particles with a pre-magnetized high-temperature superconducting bulk in a weak background field

Abstract Recent research has shown significant progress towards a full body magnetic drug delivery (MDD) system for use in targeted cancer treatments. Although many different MDD systems have been proposed to generate strong remote forces capable of rapidly changing directions at distances greater than 10 cm, current state-of-the-art technologies lack in force strength and/or degrees of freedom. Knowing that high temperature superconducting (HTS) bulks can achieve trapped fields an order of magnitude larger than ferromagnets, this work aims at numerically and experimentally evaluating the forces that can be produced by HTS bulks in a uniform magnetic field. We first use Hall probe measurements and finite element simulations to determine the magnetic field generated by an HTS pellet and show that both results are in good agreement. Using a combination of simulations and experiments, we then show that for a 14 × 6 mm YBa2Cu3O 7 − x pellet magnetized at 2 T, remote forces on superparamagnetic microparticles are maximized at background fields of ∼50 mT. In addition, the direction of the magnetic forces can be flipped by changing the direction of the applied field relative to the HTS’s magnetization. The HTS bulk was successfully used to navigate magnetic microparticles in a glass bifurcation mimicking the hepatic artery of the human liver. Finally, we show by simulation that a large HTS pellet magnetized at 5 T in a field of ∼250 mT can generate stronger forces with more degrees of freedom than the strongest forces achievable in current MDD technologies.

Flux dynamics, anisotropy in Jc and vortex phase diagram of H+-intercalated FeSe single crystal

This paper investigates the superconductivity, pinning, and vortex dynamics of FeSe before and after protonation. The study shows that, after being protonated, FeSe's superconducting critical temperature Tc has been increased to more than 40 K and the critical current density Jc has also been increased from 2.1 × 104 A/cm2 to 1.2 × 106 A/cm2, with significantly larger magnetic relaxation rates (Q). Meanwhile, the critical current density anisotropy (γ) decreases substantially while the upper critical field Hc2 increases from 13 T to 91 T after protonation. In addition, the reasons for the absence of the second peak effect in Hx-FeSe were explored. This investigation also reveals the existence of the vortex phase transition associated with the pinning behavior in protonated FeSe, demonstrated by the foot-like characteristics of resistivity. Based on these results, the vortex phase diagrams of FeSe before and after protonation were established. These findings provide important insights for exploring new high-temperature superconductors and their magnetic flux dynamics through protonation.

Design and development of dual-band superconducting filter with a novel structure

In this paper, a novel design structure of a dual-band filter is proposed. The core of the structure is to form a dual-band filter by connecting two sub-filters through a matching network. The matching network can not only improve the flexibility of the design, but also minimize the influence between the two sub-filters. Two sub-filters are designed separately, one of which is composed of interdigital resonators and the other is composed of hairpin resonators. The center frequency and bandwidth of the two passbands are flexible and controllable. Finally, a dual-band high-temperature superconducting (HTS) filter is designed and successfully fabricated on a DyBa2Cu3O7 (DyBCO) thin film on thickness of 0.5 mm LaAlO3 wafer, and the measured results are in good agreement with the simulation results.

Distinct ultrafast dynamics of bilayer and trilayer nickelate superconductors regarding the density-wave-like transitions

In addition to the pressurized high-temperature superconductivity, bilayer and trilayer nickelate superconductors Lan+1NinO3n+1 (n = 2 and 3) exhibit many intriguing properties at ambient pressure, such as orbital-dependent electronic correlation, non-Fermi liquid behavior, and density-wave transitions. Here, using ultrafast reflectivity measurement, we observe a drastic difference between the ultrafast dynamics of the bilayer and trilayer nickelates at ambient pressure. We observe a coherent phonon mode in La4Ni3O10 involving the collective vibration of La, Ni, and O atoms, which is absent in La3Ni2O7. Temperature-dependent relaxation time diverges near the density-wave transition temperature of La4Ni3O10, while it is inversely proportional to the temperature in La3Ni2O7 above ∼150 K, suggesting a dramatic difference in the density-wave states of the two compounds and a non-Fermi liquid behavior of La3Ni2O7. Moreover, we estimate the electron-phonon coupling constants to be 0.05–0.07 and 0.12–0.16 for La3Ni2O7 and La4Ni3O10, respectively, suggesting a relatively minor role of electron-phonon coupling in the electronic properties of Lan+1NinO3n+1. Our work not only sheds light on the relevant microscopic interaction but also establishes a foundation for further studying the interplay between superconductivity and density-wave transitions in nickelate superconductors.

The Abrikosov vortex structure revealed through near-field radiative heat exchange

The Abrikosov lattice is a property of type II superconductors in which normal and superconducting carriers coexist and arrange in a regular pattern. Here, we address the question on whether vortex matter, particularly the Abrikosov lattice, influences the local thermal properties of high-temperature superconductors. We find that their optical properties are not only dictated by the order parameter, but also that the near-field radiative heat flux acquires a periodic spatial structure inherited from the Abrikosov lattice. Surprisingly, we predict a radial displacement of the heat flux maxima with respect to the vortexes cores, for temperatures well below the critical one.

Dynamic resistance of a REBCO tape carrying direct current under a mixture magnetic field of AC field with DC-biased field

Abstract When the REBCO coated conductor tape carries a direct current(DC) transport current whilst exposed to the alternating current(AC) magnetic field, a DC electrical resistance can be observed, which is called “dynamic resistance”. The High Temperature Superconducting(HTS) magnet wound by the REBCO tapes is located in the HTS electrical machine as field winding carrying DC transport current. The operational environment of the HTS electrical machine involves a complex magnetic field, encompassing both AC and DC components. The interaction between the AC magnetic field and the DC transport current induces dynamic resistance and dynamic loss in the REBCO tape which is a distinctive trait of REBCO tape. Additionally, the presence of an extra DC-biased magnetic field can decrease the critical current of the REBCO tape, thereby altering its electromagnetic properties and potentially compromising its safety. As the basis of superconducting magnets, it is particularly important to study the dynamic resistance and loss distribution of the single REBCO tape under a mixture of magnetic field backgrounds, according to the real working environments in various applications. In this paper, the electromagnetic-thermal coupling model of multilayer REBCO tape based on H-formulation is built in COMSOL Multiphysics. The electromagnetic characteristics and dynamic resistance of the tape are presented when the tape is applied AC magnetic field and carries DC transport current. The effects of perpendicular and parallel DC-biased magnetic fields on the dynamic resistance and loss distribution of the REBCO tape are investigated in the paper. And the DC transport current safety margin will be observed in different applied DC-biased magnetic fields. This study comprehensively demonstrates the variation of dynamic resistance and loss distribution under a complex background magnetic field, which is significant for exploring the electromagnetic characteristics and calculating the loss of the HTS magnets in the HTS electrical machine.

CORC® wires allowing bending to 20 mm radius with 97.5% retention in critical current and having an engineering current density of 530 A mm−2 at 20 T

Abstract Low-inductance, high-field insert solenoid magnets and 20 T dipole magnets for particle accelerators require flexible cables, wound from high-temperature superconductors (HTS) such as RE-Ba2Cu3O7-δ (REBCO) coated conductors, that allow bending to a 20 mm radius without significant degradation in performance. They require an operating current of at least 5 kA and a high engineering current density (Je) exceeding 500 A/mm2 at 20 T. HTS cable technologies that target such demanding magnet applications so far haven’t been able to meet the combination of these requirements.
Here we present the development of the next generation of Conductor on Round Core (CORC®) wires that improves their bending flexibility by factor of more than 2 compared to previous generation CORC® wires. CORC® wires now allow for a bending radius of 20 mm with only 2 – 3 % performance degradation. They allow bending to a radius of 15 mm with a performance retention of 83.5 %. The performance of 30-tape CORC® wires wound from 2 mm wide REBCO tapes from SuperPower Inc, SuperOx and Shanghai Superconductor Technologies was measured at magnetic fields up to 12 T. The overall performance at high magnetic fields of the next generation of CORC® wires improved by a factor of 1.5 – 1.8, depending on the REBCO tape manufacturer. CORC® wires wound from production REBCO tapes achieved a new record Je of 751 A/mm2 at a current of 8.3 kA at 12 T, and a Je of 530 A/mm2 at a current of 5.8 kA when extrapolated to 20 T. 

Universal correlation between H-linear magnetoresistance and T-linear resistivity in high-temperature superconductors

The signature feature of the ‘strange metal’ state of high-Tc cuprates—its linear-in-temperature resistivity—has a coefficient α1 that correlates with Tc, as expected were α1 derived from scattering off the same bosonic fluctuations that mediate pairing. Recently, an anomalous linear-in-field magnetoresistance (=γ1H) has also been observed, but only over a narrow doping range, leaving its relation to the strange metal state and to the superconductivity unclear. Here, we report in-plane magnetoresistance measurements on three hole-doped cuprate families spanning a wide range of temperatures, magnetic field strengths and doping. In contrast to expectations from Boltzmann transport theory, γ1 is found to correlate universally with α1. A phenomenological model incorporating real-space inhomogeneity is proposed to explain this correlation. Within this picture, superconductivity in hole-doped cuprates is governed not by the strength of quasiparticle interactions with a bosonic bath, but by the concentration of strange metallic carriers.

Design of HTS linear phase bandpass filter based on the inline topology

Abstract Inline topology filters have the advantages of a simple structure and fewer coupling coefficients. Based on the inline topology, this paper constructs a phase compensation topology of the filter, which can independently and controllably introduce two types of transmission zeros (TZs), and is convenient to realize the Chebyshev-like function response and compensate group delay. The finite frequency transmission zero is directly introduced through the source and load (S/L), and the real zero point is introduced and adjusted through the cross-coupling unit of the main path in this inline phase compensation topology. The two types of TZs can be introduced and regulated independently, so the side-band suppression and group delay compensation can be freely adjusted. A High-temperature superconducting (HTS) filter with inline is designed and processed with a typical structure based on application requirements. The filter introduces two pairs of symmetrical real TZs to improve sideband rejection and a pair of real TZs to control group delays to realize the linear phase. In addition, it has a small size and straightforward construction, and the results of the full-wave analysis method and the theoretical analysis approach match well with the measured results of the frequency response characteristics.

Quantum size effects in ultra-thin YBa2Cu3O7 − x films

The d-wave symmetry of the order parameter with zero energy gap in nodal directions stands in the way of using high-temperature superconductors for quantum applications. We investigate the symmetry of the order parameter in ultra-thin YBa2Cu3O7 − x (YBCO) films by measuring the electrical transport properties of nanowires aligned at different angles relative to the main crystallographic axes. The anisotropy of the nanowire critical current in the nodal and antinodal directions reduces with the decrease in the film thickness. The Andreev reflection spectroscopy of the nanoconstrictions shows the presence of a thickness-dependent energy gap that does not exist in bulk YBCO. We find that the thickness-dependent energy gap appears due to the quantum size effects in ultra-thin YBCO films that open the energy gap along the entire Fermi surface. The fully gapped state of the ultra-thin YBCO films makes them a promising platform for quantum applications, including quantum computing and quantum communications.

Fundamental study on performances of fiber-superconducting composite CORC cable: electromagnetic, thermal, mechanical and quench behaviors

Abstract Common terminal voltage measurement can be hardly applied to detect quenches in long high temperature superconducting (HTS) conductor on round core (CORC) cable because not only the HTS normal zone propagation velocity (NZPV) is low but also immobilizing a large number of voltage leads is inconvenient. Distributed optical fiber sensing (DOFS) technology is a promising method for quench detection of long superconductors. To sense the thermal changes of CORC cables during quenches more directly and prevent optical fibers from damages by external stress, a fiber-superconducting composite (FSC) CORC cable was fabricated. For this cable, three optical fibers were placed in three grooves of the copper core respectively, then three HTS tapes were spirally wound on the copper core in sequence. Comparing to a traditional CORC cable, obviously, the FSC CORC cable structure has been changed. To promote FSC CORC cable engineering applications, it is necessary to study the fundamental performance of the cable. In this paper, we investigated the electromagnetic, thermal and mechanical properties of the FSC CORC cable by comparing those with a common one. The results demonstrated that, compared to the common one, the magnetic distribution of the FSC CORC cable hardly changed, but the current distribution of the copper core in the FSC CORC cable slightly changed which led to decreases of transport AC loss, in addition, the thermal characteristics of the FSC CORC cable was slightly changed and the bending tolerance ability of the cables reduced within a bending diameter range of 15 cm. What’s more, the embedded optical fibers combined with DOFS system are successfully used to detect the temperature changes of the cable surface. Finally, to study the quench behaviors of the cable, we built a quench detection platform, which equips with a voltage acquisition system, a thermocouple temperature acquisition system and the DOFS system. By using the platform to detect the quenches of the FSC CORC cable, minimum quench energy of the cable and NZPV of the tape and cable at different currents was tested.

General Properties of Conventional and High-Temperature Superconductors

In our review, we analyze the scaling of the condensation energy EΔ divided by γ, EΔ/γ≃N(0)Δ12/γ, and quasiparticles of both conventional and unconventional superconductors, where N(0) is the density of states at zero temperature T=0, Δ1 is the maximum value of the superconducting gap, and γ is the Sommerfeld coefficient. It is shown that Bogoliubov quasiparticles act in superconducting states of unconventional and conventional superconductors. At the same time, quasiparticles are also present in the normal state of unconventional superconductors. We briefly describe the difference between unconventional superconductors and conventional ones, such as the resistivity in normal states and the difference in superfluid density in superconducting states. For the first time, we theoretically show that the universal scaling of EΔ/γ∝Tc2 applies equally to both conventional and unconventional superconductors. Our consideration is based on two experimental facts: Bogoliubov quasiparticles act in conventional and non-conventional superconductors and the corresponding flat band is deformed by the non-conventional superconducting state. As a result, our theoretical observations based on the theory of fermion condensation agree well with the experimental facts.

High-Temperature Superconductivity in Perovskite Hydride Below 10GPa.

Hydrogen and hydride materials have long been considered promising materials for high-temperature superconductivity. However, the extreme pressures required for the metallization of hydrogen-based superconductors limit their applications. Here, a series of high-temperature perovskite hydrides is designed that can be stable within 10GPa. The research covered 182 ternary systems and ultimately determined that eight new compounds are stable within 20GPa, of which five exhibited superconducting transition temperatures exceeding 120 K within 10GPa, including KGaH3 (146 K at 10GPa), RbInH3 (130 K at 6GPa), CsInH3 (153 K at 9GPa), RbTlH3 (170 K at 4GPa) and CsTlH3 (163 K at 7GPa). Excitingly, KGaH3 and RbGaH3 are thermodynamically stable at 50GPa. Among these perovskite hydrides, alkali metals are responsible for providing a fixed amount of charge and supporting alloy framework composed of hydrogen and IIIA group elements to maintain stable crystal structure, while the cubic hydrogen alloy framework formed by IIIA group elements and hydrogen is crucial for high-temperature superconductivity. This work will inspire further experimental exploration and take an important step in the exploration of low-pressure stable high-temperature superconductors.

Design of superconducting compounds at lower pressure via intercalating XH$_4$ molecules (X = B, C, and N) into fcc lattices

Abstract Recently, many encouraging experimental processes have been achieved in ternary hydrides superconductors under high pressure. However, the extreme pressure required is indeed a challenge for practical application, which promotes a further exploration for high temperature (T c) superconductors at relatively low pressure. Herein, we performed a systematic theoretical investigation on a serious of ternary hydrides with stoichiometry AX$_2$H$_8$, which is constructed by interacting molecular XH$_4$ (B, C, and N) into the fcc metal A lattice under low-pressure range of 0-150 GPa. We uncovered five compounds which are dynamically stable below 100 GPa, e.g., AcB$_2$H$_8$ (25 GPa), LaB$_2$H$_8$ (40 GPa), RbC$_2$H$_8$ (40 GPa), CsC$_2$H$_8$ (60 GPa), and SrC$_2$H$_8$ (65 GPa). Among these, AcB$_2$H$_8$, which is energetically stable above 2.5 GPa, exhibits the highest T c value of 32 K at 25 GPa. The superconductivity originates mainly from the coupling between the electron of Ac atoms and the associated low-frequency phonons, distinct from the previous typical hydrides with H-derived superconductivity. Our results shed light on the future exploration of superconductivity among ternary compounds at low pressure.

Strong Pairing Originated from an Emergent Z_{2} Berry Phase in La_{3}Ni_{2}O_{7}.

The recent discovery of high-temperature superconductivity in La_{3}Ni_{2}O_{7} offers a fresh platform for exploring unconventional pairing mechanisms. Starting with the basic argument that the electrons in d_{z^{2}} orbitals nearly form local moments, we examine the effect of the Hubbard interaction U on the binding strength of Cooper pairs based on a single-orbital bilayer model with intralayer hopping t_{∥} and interlayer superexchange J_{⊥}. By extensive density matrix renormalization group calculations, we observe a remarkable enhancement in binding energy as much as 10-20 times larger with U/t_{∥} increasing from 0 to 12 at J_{⊥}/t_{∥}∼1. We demonstrate that such a substantial enhancement stems from a kinetic-energy-driven mechanism. Specifically, a Z_{2} Berry phase will emerge at large U due to the Hilbert space restriction (Mottness), which strongly suppresses the mobility of single particle propagation as compared to U=0. However, the kinetic energy of the electrons (holes) can be greatly restored by forming an interlayer spin-singlet pairing, which naturally results in a superconducting state even for relatively small J_{⊥}. An effective hard-core bosonic model is further proposed to estimate the superconducting transition temperature at the mean-field level.

Avoided metallicity in a hole-doped Mott insulator on a triangular lattice

Doping of a Mott insulator gives rise to a wide variety of exotic emergent states, from high-temperature superconductivity to charge, spin, and orbital orders. The physics underpinning their evolution is, however, poorly understood. A major challenge is the chemical complexity associated with traditional routes to doping. Here, we study the Mott insulating CrO2 layer of the delafossite PdCrO2, where an intrinsic polar catastrophe provides a clean route to doping of the surface. From scanning tunnelling microscopy and angle-resolved photoemission, we find that the surface stays insulating accompanied by a short-range ordered state. From density functional theory, we demonstrate how the formation of charge disproportionation results in an insulating ground state of the surface that is disparate from the hidden Mott insulator in the bulk. We demonstrate that voltage pulses induce local modifications to this state which relax over tens of minutes, pointing to a glassy nature of the charge order.

Comparison of Levitation Properties between Bulk High-Temperature Superconductor Blocks and High-Temperature Superconductor Tape Stacks Prepared from Commercial Coated Conductors.

Bulk high-temperature superconductors (HTSs) such as REBa2Cu3O7-x (REBCO, RE = Y, Gd) are commonly used in rotationally symmetric superconducting magnetic bearings. However, such bulks have several disadvantages such as brittleness, limited availability and high costs due to the time-consuming and energy-intensive fabrication process. Alternatively, tape stacks of HTS-coated conductors might be used for these devices promising an improved bearing efficiency due to a simplification of manufacturing processes for the required shapes, higher mechanical strength, improved thermal performance, higher availability and therefore potentially reduced costs. Hence, tape stacks with a base area of (12 × 12) mm2 and a height of up to 12 mm were prepared and compared to commercial bulks of the same size. The trapped field measurements at 77 K showed slightly higher values for the tape stacks if compared to bulks with the same size. Afterwards, the maximum levitation forces in zero field (ZFC) and field cooling (FC) modes were measured while approaching a permanent magnet, which allows the stiffness in the vertical and lateral directions to be determined. Similar levitation forces were measured in the vertical direction for bulk samples and tape stacks in ZFC and FC modes, whereas the lateral forces were almost zero for stacks with the REBCO films parallel to the magnet. A 90° rotation of the tape stacks with respect to the magnet results in the opposite behavior, i.e., a high lateral but negligible vertical stiffness. This anisotropy originates from the arrangement of decoupled superconducting layers in the tape stacks. Therefore, a combination of stacks with vertical and lateral alignment is required for stable levitation in a bearing.

High temperature superconductor Na2B2H stabilized by hydrogen intercalation under ambient pressure

High temperature superconductor Na2B2H stabilized by hydrogen intercalation under ambient pressure

Enhancing dynamic stability of HTS maglev systems with preloading method

High temperature superconducting (HTS) bulks have strong flux pinning capabilities and are widely used in various fields. Their self-stabilizing characteristics also provide new ideas for ultra-high-speed rail transit. For HTS maglev systems, operational stability, curve negotiation and safety when subjected to external forces are very important. Due to the hysteresis effect of superconducting bulks, they do not always return to their initial positions after deviating from the levitated position in an alternative external magnetic field. In some cases, the levitation system can be destroyed. Studies have shown that preloading can enhance quasi-static levitation performance. Therefore, this paper conducts a detailed analysis of the quasi-static levitation and guidance forces of HTS bulks above a Halbach permanent magnet guideway (PMG) under conditions with and without preloading. Additionally, the dynamic responses of the HTS bulks under lateral or vertical pulsed excitations are studied, with a particular focus on the final equilibrium position offset after disturbance. The results indicate that preloading can suppress the attenuation of the levitation force, enhance the guidance performance, and raise stiffness in both lateral and vertical directions. It also effectively suppresses position deviation from disturbance and increases the maximum excitation force threshold for system instability. This study provides practical insights for HTS maglev applications.

Synthesis of HTSP Y1<sub>1-x</sub>Fe<sub>x</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> by Sol-Gel and Solid-Phase Methods

A modified version of using of the sol-gel process at the initial stage of the synthesis of a high-temperature superconductor (HTSC) Y1-xFexBa2Cu3Oy with low Fe doping is proposed. The properties of samples obtained by sol-gel and solid-state synthesis have been compared. It has been shown that a more uniform distribution of the dopant throughout the volume of the sol-gel samples makes it possible to obtain materials with improved microstructural and performance characteristics.