Bulk Superconductors Research Articles

NbReSi: A noncentrosymetric superconductor with large upper critical field

We report the discovery of superconductivity in noncentrosymmetric NbReSi, which crystallizes in a hexagonal ZrNiAl-type crystal structure with space group $P\bar{6}2m$ (No.~189). Bulk superconductivity, with $T_c$ = 6.5 K was characterized via electrical-resistivity, magnetization, and heat-capacity measurements. The low-temperature electronic specific heat suggests a fully gapped superconducting state in NbReSi, while a large upper critical field of $\mu_0H_\mathrm{c2}(0)$ $\sim$ 12.6 T is obtained, which is comparable to the weak-coupling Pauli limit. The electronic band-structure calculations show that the density of states at the Fermi level are dominated by Re and Nb $d$-orbitals, with a sizeable band splitting induced by the antisymmetric spin-orbit coupling. NbReSi represents another candidate material for revealing the puzzle of time-reversal symmetry breaking observed in some Re-based superconductors and its relation to the lack of inversion symmetry.

Superconductivity from Charge Order in Cuprates

Superconductivity in layered cuprates is induced by doping holes into a parent antiferromagnetic insulator. It is now recognized that another common emergent order involves charge stripes, and our understanding of the relationship between charge stripes and superconductivity has been evolving. Here we review studies of 214 cuprate families obtained by doping La$_2$CuO$_4$. Charge-stripe order tends to compete with bulk superconductivity; nevertheless, there is plentiful evidence that it coexists with two-dimensional superconductivity. This has been interpreted in terms of pair-density-wave superconductivity, and the perspective has shifted from competing to intertwined orders. In fact, a new picture of superconductivity based on pairing within charge stripes has been proposed, as we discuss.

A reconstructed three-dimensional HTS bulk electromagnetic model considering J c spatial inhomogeneity and its implementation in a bulks’ combination system

High-temperature superconducting (HTS) bulks in HTS Maglev systems are always arrayed in a combination to make full use of the applied magnetic field of the permanent magnet guideway (PMG). An excellent combination scheme improves the overall levitation and guidance performance significantly. In this paper, a three-dimensional (3D) electromagnetic model of the real HTS-PMG maglev system with an HTS bulk array was established. This model comprehensively expresses the influence of various factors on the E – J relationship and the 3D spatial distribution of J c, including internal factors such as the inhomogeneity and anisotropy of electromagnetic characteristics, as well as external factors such as applied magnetic field and working temperature. A ternary function was proposed to describe the uneven distribution of J c caused by the bulk’s growth process, which is an interesting phenomenological modeling attempt. In the simulations of the bulks’ combinations, perfect magnetic conductor boundary conditions were applied on the contact surface to simulate two bulks touching each other. Besides, the research target includes reproducing the shapes, the orientations, and the combination scheme of HTS bulks in the real PMG magnetic field. The calculation results of levitation force of the cylindrical bulk under different spatial orientations above the PMG were compared with the experimental results, through which the accuracy of the model was verified. On this basis, the influence of the magnetic field generated by the superconducting current on the nearby bulk was further explored. It was found that this magnetic field has a small contribution to the total levitation force and a relatively obvious influence on the guidance force. When the lateral displacement is large, such as 5 mm, the magnetic field generated by the superconducting current slightly increases the total guidance force stiffness. According to more simulated conditions, some optimization strategies on bulk combinations were proposed. This work provides not only a 3D descriptive model for fitting the real multi-bulk-combination maglev scenarios but also some optimization strategies for the HTS maglev transportation applications.

The magnetic and levitation characteristics of single-grain YBaCuO and GdBaCuO-Ag bulk superconductors in high magnetic fields

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

Group-9 Transition-Metal Suboxides Adopting the Filled-Ti2Ni Structure: A Class of Superconductors Exhibiting Exceptionally High Upper Critical Fields

Ti2Ni and the related η-carbide structure are known to exhibit various intriguing physical properties. The Ti2Ni structure with the cubic space group Fd3̅m is surprisingly complex, consisting of a unit cell with 96 metal atoms. The related η-carbide compounds correspond to a filled version of the Ti2Ni structure. Here, we report on the structure and superconductivity in the η-carbide-type suboxides Ti4M2O with M = Co, Rh, and Ir. We have successfully synthesized all three compounds in the single-phase form. We found all three compounds to be type-II bulk superconductors with transition temperatures of Tc = 2.7, 2.8, and 5.4 K and with normalized specific heat jumps of ΔC/γTc = 1.65, 1.28, and 1.80 for Ti4Co2O, Ti4Rh2O, and Ti4Ir2O, respectively. We found that all three superconductors exhibit high upper critical fields. Particularly noteworthy in this regard is Ti4Ir2O with an upper critical field of μ0Hc2(0) = 16.06 T, which exceeds by far the weak-coupling Pauli limit─widely considered as the maximal upper critical field─of μ0HPauli = 9.86 T. The role of the void-filling light atom X has so far been uncertain for the overall physical properties of these materials. Herein, we have successfully grown single crystals of Ti2Co. In contrast to the metallic η-carbide-type suboxides Ti4M2O, we found that Ti2Co displays a semimetallic behavior down to 0.75 K. Below 0.75 K, we observe a broad decrease in the resistivity, which can most likely be attributed to an onset of a superconducting transition at lower temperatures. Hence, the octahedral void-filling oxygen plays a crucial role in the overall physical properties, even though its effect on the crystal structure is small. Our results indicate that the design of new superconductors by incorporation of electron–acceptor atoms may in the Ti2Ni-type structures and other materials with crystallographic void position be a promising future approach. The remarkably high upper critical fields, in this family of compounds, may furthermore spark significant future interest.

Anomalous broadening of specific heat jump at T c in high-entropy-alloy-type superconductor TrZr2

A high-entropy-alloy-type (HEA-type) superconductor is new category of highly disordered superconductors. Therefore, finding brand-new superconducting characteristics in the HEA-type superconductors would open new avenue to investigate the relationship between structural disorder and superconductivity. Here, we report on the remarkable broadening of specific heat jump near a superconducting transition tempreature (T c) in transition-metal zirconides (TrZr2) with different mixing entropy (ΔS mix) at the Tr site. With increasing ΔS mix, the superconducting transition seen in specific heat became broader, whereas those seen in magnetization were commonly sharp. Therefore the broadening of specific heat jump would be related to the microscopic inhomogeneity of the formation of Cooper pairs behind the emergence of bulk superconductivity states.

Superconductivity in MgTa2S5

Superconductivity in the new compound, MgTa2S5, is reported. Its crystal structure was indexed to space group C2/m, which is monoclinic with lattice parameters a = 5.784(5) Å, b = 12.680(3) Å, and c = 6.106(5) Å, with β = 112.64∘. Electrical resistivity reveals metallic behavior with ρ(296 K) = 5.2 mΩ cm and bulk superconductivity below Tc = 1 K. Measurements of the specific heat C reveal the electronic specific heat coefficient γ = 11.1(5) mJ/mol K2, a jump in C at Tc illustrating bulk superconductivity, and an energy gap associated with the superconducting state of Eg = 0.25(3) meV. MgTa2S5 can be classified as a BCS superconductor. An unidentified minority phase present in the sample (∼ 4%) exhibits a superconducting phase transition near 2.6 K.

The superconductivity and transport properties in FeTe with S addition

In the past few years, iron chalcogenide compounds have attracted considerable attentions due to its unique superconductivity and simplest structure. Till now, many studies have been devoted to explore the superconductivity in iron chalcogenides, including FeSe, FeTe, FeS and their derivatives produced by intermediate doping. However, compared with FeSe, although the superconductivity in S doped FeTe has been widely studied, very few attempts have been reported on the transport properties for this material. Herein the evolution of the superconductivity and the Hall effect up to high S addition levels in FeTe1-xSx (0 ≤ x ≤ 0.5) were studied. It suggests that S substitution for Te sites can effectively suppress the antiferromagnetic ordering and introduce bulk superconductivity in FeTe. The highest Tc ∼9.0 K is achieved in FeTe0.8S0.2 with nominal S content. Hall effect suggests that S addition in FeTe undergoes a reconstruction of hole-type Fermi surface, indicating doping or enhancement of scattering of hole carriers. This work systemically studied the superconductivity of FeTe with S addition and proposes complementary understanding for the intrinsic transport mechanism of iron-based superconductivity.

Analysis of Electromagnetic Properties of Bulk Superconductors.

In the present study, a YBa₂Cu₃O7-y bulk superconductor added with 5~10 wt% Ag was fabricated employing Sm123 as a seed to produce a superconductive single crystal. Metallic silver was added to the single crystal of YBa₂Cu₃O7-y to remove defects such as cracks and pores. Electromagnetic properties of the bulk superconductor at 77 K were analyzed based on relationships of magnetic levitation, trapped magnetic force, and critical current density. The critical current density of the superconductor at 77 K and 0 T was 3.53 × 10⁴ A/cm². Discontinuous points in the distribution of magnetic field lines were not observed, implying that these two specimens grew well as a single crystal without specific weak links. For the growth of a superconductive nano crystal employing slow cooling at temperature of formation of 123 phase, superconductive nano crystals were aligned in a-b direction, the direction of peak current flow. The peak value of the trapped magnetic force of the YBa₂Cu₃O7-y superconductor specimen was 3.23 kG. Using the FC method, peak forces of attraction and repulsion were 21.696 N and 70.168 N, respectively.

The influence of CeO2 addition on microstructure and superconducting properties of GdBCO-Ag single grain bulk superconductors

Bulk single-grain GdBCO superconductors (nominal composition 1 mol GdBa2Cu3O7-δ + ½ mol Gd2BaCuO5 + 20 wt% Ag2O + Z wt% CeO2 (Z = 0.4, 1.0, 1.6) grown using the top-seeded melt-grow process are studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy and magnetic measurement of local superconducting properties. The amount of CeO2 added is shown to have a significant effect on thermal behaviour, phase composition, microstructure and local superconducting properties. The observed behaviour is explained by the dissolution of Ce in the melt L' formed by monotectic melting of the samples. Ce dissolved in melt L' reduces the substitution of Ba by Gd in the Gd123 crystal lattice. This effect causes an increase in the superconducting transition temperature Tc with added CeO2, an increase in Tc with distance from the seed and influences the critical current density by chemical pinning. The obtained results open a new effective way to improve the superconducting properties of LREBCO bulk single-grain superconductors grown in air.

Superconductivity with Topological Non-trivial Surface States in NbC

Quantum materials with non-trivial band topology and bulk superconductivity are considered superior materials to realize topological superconductivity. In this regard, we report detailed density functional theory (DFT) calculations and Z2 invariants for the NbC superconductor, exhibiting its band structure to be topologically non-trivial. Bulk superconductivity at 8.9 K is confirmed through DC magnetization measurements under field cooled (FC) and zero field cooled (ZFC) protocols. This superconductivity is found to be of type II nature as revealed by isothermal M-H measurements, and thus the Ginzburg–Landau parameter is calculated. A large intermediate state is evident from the phase diagram, showing NbC to be a strong type-II superconductor. Compared with earlier reports on superconducting NbC, a non-monotonic relationship of critical temperature with lattice parameters is seen. In conclusion, NbC is a type-II around 10 K superconductor with topological non-trivial surface states.

Tunneling and break junction spectroscopy of the ambient-pressure semiconducting and superconducting gap structures in the ladder compound (Sr, Ca)14Cu24O41

The ladder-chain compound ${(\mathrm{Sr}, \mathrm{Ca})}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ is a semiconductor at ambient pressure, but becomes a bulk superconductor above the pressure of about 3 GPa. Since the compound is at the verge of the metal-insulator transition, it is reasonable to make tunnel measurements to probe the electronic density of states in its subtleties. We present the results of such measurements carried out at ambient pressure. The break junction (BJ) tunneling gives evidence for the apparent typical gap $2\mathrm{\ensuremath{\Sigma}}$ of about 140 meV at temperature $T$, equal to 4 K. The gap is smeared out at ${T}^{*}\ensuremath{\approx}90--100$ K. We interpret the gap as that induced by the charge density wave (CDW) formation, although its $T$-dependence differs from the usually observed CDW-like mean-field behavior. Quite unexpectedly, BJ spectra also exhibit distinct zero-bias peak accompanied by the low-energy gaps of $2\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}4--8$ meV immediately after BJ are formed at 4 K. The thermally driven disappearance of this apparently superconducting structure at ${T}_{c}\ensuremath{\approx}7--13$ K is consistent with the conventional properties of superconducting tunnel junctions. The resultant ratio $\mathrm{\ensuremath{\Delta}}/{T}_{c}$ is consistent with similar observed values for a high-${T}_{c}$ cuprate superconductor. Therefore, we attribute this feature as well as the Josephson-like zero-bias conductance peak to the superconductivity induced at the freshly created BJ surface of the ${(\mathrm{Sr}, \mathrm{Ca})}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, which is semiconducting in the sample bulk. Our additional scanning tunneling microscopy data testify that the cracked atomic surface of this compound is substantially modified, which might be the reason for the superconductivity appearance.

A reliable technique to fabricate superconducting joints between single grain, Y–Ba–Cu–O bulk superconductors

The production of large (RE)Ba–Cu–O single grains ((RE)BCO), where RE = Y, Gd or Sm, of complex geometries is presently limited by the intrinsic slowness of the grain growth process. Additionally, the shapes achievable using established melt processing are constrained by the small number of post-processing techniques available. These materials are brittle and hard, which makes machining a difficult task and largely eliminates the possibility of producing highly intricate shapes. An alternative to this slow and inflexible growth process would be to join many small single grains to form one large composite grain, connected by high-performance superconducting joints. A reliable joining technique would also overcome the need for the careful and time-consuming post-growth machining processes. In this work we report on the use of single grain YBCO–Ag as an interface medium to achieve superconducting joints between (RE)BCO bulks. This joining technique is relatively quick and does not require tight process parameter control as there is no need to re-grow the interface joining material. We report on six joints produced from samples cut and joined in a variety of orientations. In addition, a joint was produced using bulk YBCO from two independent single grains. The trapped field properties of the resulting joined sample were measured and the microstructure at the joint was examined. We show that this simple but effective joining technique makes it possible to produce multiple composite grains with comparable superconducting properties to those of a single grain of the same size.

Fully-staggered-array bulk Re-Ba-Cu-O short-period undulator: large-scale 3D electromagnetic modelling and design optimization using A-V and H-formulation methods

The development of a new hard x-ray beamline I-TOMCAT equipped with a 1 m long short-period bulk high-temperature superconductor undulator (BHTSU) has been scheduled for the upgrade of the Swiss Light Source at the Paul Scherrer Institute. The very hard x-ray source generated by the BHTSU will increase the brilliance at the beamline by over one order of magnitude in comparison to other state-of-the-art undulator technologies and allow experiments to be carried out with photon energies in excess of 60 keV. One of the key challenges for designing a 1 m long (100 periods) BHTSU is the large-scale simulation of the magnetization currents inside 200 staggered-array bulk superconductors. A feasible approach to simplify the electromagnetic model is to retain five periods from both ends of the 1 m long BHTSU, reducing the number of degrees of freedom to the scale of millions. In this paper, the theory of the recently-proposed 2D A -V formulation-based backward computation method is extended to calculate the critical state magnetization currents in the ten-period staggered-array BHTSU in 3D. The simulation results of the magnetization currents and the associated undulator field along the electron beam axis are compared with the well-known 3D H -formulation and the highly efficient 3D H -ϕ formulation method, all methods showing excellent agreement with each other as well as with experimental results. The mixed H -ϕ formulation avoids computing the eddy currents in the air subdomain and is significantly faster than the full H -formulation method, but is slower in comparison to the A -V formulation-based backward computation. Finally, the fastest and the most efficient A -V formulation, implemented in ANSYS 2020R1 Academic, is adopted to optimize the integrals of the undulator field along the electron beam axis by optimizing the sizes of the end bulks.

Anderson pseudospin and Superradiant Superconductivity revisited

Using Anderson pseudospins (Anderson, 1958; Bardeen et al., 1957), I suggested in 2012 (Baskaran, 2012) superradiant superconductivity (SRSC) and related Dicke phenomena in bulk superconductors. It was a response to a report from Cavalleri’s lab (Kaiser et al., 2012; Fausti et al., 2011), of transient room temperature superconductivity in YBCO, when pumped by 20 THz laser pulses. In my minimal model, Anderson pseudospins in k-space in a bulk superconductor were coupled to single polariton mode. The model was adapted to the pseudogap normal state of YBCO to explain observed transient superconductivity. We also pointed out, possibility of other Dicke phenomena, (i) spontaneous superradiance above a critical polariton matter coupling, with no pumping, (ii) enhanced quantum entanglement near the critical coupling and (iii) superfluoresence. Here we revisit our early work. Recent discovery by Ebbesens group (Thomas et al., 2019) of large increase of superconducting Tc from 30 K to 45 K in K3C60 via specially designed plasmon–phonon-polariton mode, but with no external pumping seems to be in line with our early prediction. Relevance of SRSC to developments, including other superradiant matters and Higgs Spectroscopy is pointed out.

Superconductivity in LiGa2Ir Heusler type compound with VEC\u2009=\u200916

Polycrystalline LiGa2Ir has been prepared by a solid state reaction method. A Rietveld refinement of powder x-ray diffraction data confirms a previously reported Heusler-type crystal structure (space group Fm-3m, No. 225) with lattice parameter a = 6.0322(1) Å. The normal and superconducting state properties were studied by magnetic susceptibility, heat capacity, and electrical resistivity techniques. A bulk superconductivity with Tc = 2.94 K was confirmed by detailed heat capacity studies. The measurements indicate that LiGa2Ir is a weak-coupling type-II superconductor ({uplambda }e–p = 0.57, {Delta }C/{upgamma }Tc = 1.4). Electronic structure, lattice dynamics, and the electron–phonon interaction are studied from first principles calculations. Ir and two Ga atoms equally contribute to the Fermi surface with a minor contribution from Li. The phonon spectrum contains separated high frequency Li modes, which are seen clearly as an Einstein-like contribution in the specific heat. The calculated electron–phonon coupling constant {uplambda }e–p = 0.68 confirms the electron–phonon mechanism for the superconductivity. LiGa2Ir and recently reported isoelectronic LiGa2Rh are the only two known representatives of the Heusler superconductors with the valence electron count VEC = 16.

Prediction of superconductivity at 70 K in a pristine monolayer of LiBC

Search of high-temperature superconductors has gained huge impetus since the discovery of superconductivity in bulk $\mathrm{Mg}{\mathrm{B}}_{2}$. These efforts led to the synthesis of high-${T}_{C}$ materials in the megabar pressure region. However, the ultimate goal of a room-conditions superconductor is still elusive. Toward this, a class of two-dimensional (2D) superconductors is emerging as a fertile field of research. In this paper, by solving fully anisotropic Migdal-Eliashberg equations, we show that a pristine monolayer (ML) of LiBC will be a Bardeen-Cooper-Schrieffer-type superconductor with a record-breaking ${T}_{C}$ of 70 K among pure 2D superconductors. The critical temperature could be further increased by hydrogenation of the ML. Analysis of the electronic properties indicates the partial change of B-C covalent bonding from $s{p}^{2}$ to $s{p}^{3}$ type on bulk-to-ML transformation. This paper presents a proposal to metalize the LiBC system, which was long been predicted to show superconductivity in its bulk form with 50% Li site vacancies. This system might be useful for the design and development of high-${T}_{C}$ 2D superconductors that could be applied in devices like quantum interferometers, superconducting qubits, or superconducting transistors.

Dynamic Characteristics of a YBCO Bulk Above an Electromagnet Guideway

For high-temperature superconducting (HTS) maglev, an electromagnet guideway unit (EMGU) that can form an electromagnet guideway (EMG) with a small gap, or even no gap, between EMGUs has been designed. The longitudinal magnetic fields along a single EMGU and two EMGUs arranged in a line were first investigated through measurement and simulation. The experimentally measured data validated the simulation results from a three-dimensional (3D) EMGU model implemented in COMSOL Multiphysics, indicating that the model is reliable and can be used for further studies. The dynamic responses of a high-temperature superconducting (HTS) bulk above a single EMGU and two EMGUs arranged in a line, including the dynamic levitation force (LF) and traveling directional force (TDF), under different operating conditions were investigated through experiment and simulation using a segregated H-formulation model. The magnetic field and current density distributions inside the superconductor are affected by the external magnetic field generated by the EMGU and are responsible for the dynamic characteristics. Finally, the segmented instant excitation (SIE) mode was investigated through simulation, which shows it is feasible by coordinating the currents of EMGUs.

Bulk superconductivity and Pauli paramagnetism in nearly stoichiometric CuCo2S4

It has long remained elusive whether CuCo$_{2}$S$_{4}$ thiospinel shows bulk superconductivity. Here we clarify the issue by studying on the samples of sulfur-deficient CuCo$_{2}$S$_{3.7}$ and sulfurized CuCo$_{2}$S$_{4}$. The sample CuCo$_{2}$S$_{3.7}$ has a smaller lattice constant of $a=9.454$ {\AA}, and it is not superconducting down to 1.8 K. After a full sulfurization, the $a$ axis of the thiospinel phase increases to 9.475 {\AA}, and the thiospinel becomes nearly stoichiometric CuCo$_{2}$S$_{4}$, although a secondary phase of slightly Cu-doped CoS$_2$ forms. Bulk superconductivity at 4.2 K and Pauli paramagnetism have been demonstrated for the sulfurized CuCo$_{2}$S$_{4}$ by the measurements of electrical resistivity, magnetic susceptibility, and specific heat.

Improved trapped field performance of single grain Y‐Ba‐Cu‐O bulk superconductors containing artificial holes

AbstractThe intrinsic mechanical properties of single‐grain RE‐Ba‐Cu‐O bulk high‐temperature superconductors can be improved by employing a thin‐wall geometry. This is where the samples are melt‐processed with a predefined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin‐wall YBCO disks were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO disks, the thin‐wall YBCO disks displayed an average tensile strength that is 93% higher when the holes were filled with Stycast epoxy resin. This implies a thin‐wall sample should, in theory, be able to sustain a trapped field that is 39% higher without exceeding the mechanical limit of the sample. High‐field magnetization experiments were performed by applying magnetization fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetized with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin‐wall YBCO sample survived all magnetization cycles, including a maximum magnetization field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field‐cooling the thin‐wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement.