Critical Magnetic Field Research Articles

Mechanical properties and application of superconducting materials of Nb3Sn

Nb3Sn is one of the most promising low temperature superconducting materials and its high critical current density, high critical magnetic field strength and high critical transition temperature have attracted a lot of attention in many application areas. However, the superconductivity of Nb3Sn is strongly sensitive to its mechanical behaviour. The strain and torque arise from tension during cabling and electromagnetic forces during working operation can affect the critical performance of the strand. In this paper, the development of superconducting materials was firstly introduced in a brief way. Subsequently, the paper focused on several experiments to test the mechanical properties. Devices such as Pacman and TRASIS are used to measure the axial strain/stress, transverse force, spatial periodic contact loading cycles and periodic bending. In the next section, the paper introduced the applications and finally drew a conclusion. These results shed light on guiding future studies focusing on Nb3Sn and lay a foundation for subsequent mechanical studies of Nb3Sn.

Vortex matter and critical magnetic fields in mesoscopic superconducting strips

As compared with bulk materials, superconducting strips with lateral dimensions limited to the mesoscopic region exhibit non-trivial properties, among which the critical magnetic fields related to both vortex penetration and full vortex expulsion still remain elusive. By using low-temperature scanning Hall probe microscope, the critical magnetic fields are studied experimentally in a series of superconducting Pb strips with different widths. It is found that the penetration magnetic field follows a power law dependence with strip width, and vortices can only penetrate the strips when the energy barrier at the edges is completely suppressed. In the field-cooling process, vortices are fully expelled from the strips below , above which the number of trapped vortices linearly increases with magnetic field. Compared with various theoretical predictions, we have found that the experimentally observed corresponds to the field at which the Gibbs free energy in the strip center is minimized. Our study provides important implications for designing nanostructured devices with superconducting strips.

Emergent weak antilocalization and wide-temperature-range electronic phase diagram in epitaxial RuO2 thin film

Binary ruthenium dioxide (RuO2) has gradually attracted much attention in condensed matter physics and material sciences due to its various intriguing physical properties, such as strain-induced superconductivity, anomalous Hall effect, collinear anti-ferromagnetism, etc. However, its complex emergent electronic states and the corresponding phase diagram over a wide temperature range remain unexplored, which is critically important to understanding the underlying physics and exploring its final physical properties and functionalities. Here, through optimizing the growth conditions by using versatile pulsed laser deposition, high-quality epitaxial RuO2 thin films with clear lattice structure are obtained, upon which the electronic transport is investigated, and emergent electronic states and the relevant physical properties are unveiled. Firstly, at a high-temperature range, it is the Bloch–Grüneisen state, instead of the common Fermi liquid metallic state, that dominates the electrical transport behavior. Moreover, the recently reported anomalous Hall effect is also revealed, which confirms the presence of the Berry phase in the energy band structure. More excitingly, we find that above the superconductivity transition temperature, a new positive magnetic resistance quantum coherent state with an unusual dip as well as an angel-dependent critical magnetic field emerges, which can be attributed to the weak antilocalization effect. Lastly, the complex phase diagram with multiple intriguing emergent electronic states over a wide temperature range is mapped. The results greatly promote the fundamental physics understanding of the binary oxide RuO2 and provide guidelines for its practical applications and functionalities.

Review of Single Crystal Synthesis of 11 Iron-Based Superconductors.

The 11 system in the iron-based superconducting family has become one of the most extensively studied materials in the research of high-temperature superconductivity, due to their simple structure and rich physical properties. Many exotic properties, such as multiband electronic structure, electronic nematicity, topology and antiferromagnetic order, provide strong support for the theory of high-temperature superconductivity, and have been at the forefront of condensed matter physics in the past decade. One noteworthy aspect is that a high upper critical magnetic field, large critical current density and lower toxicity give the 11 system good application prospects. However, the research on 11 iron-based superconductors faces numerous obstacles, mainly stemming from the challenges associated with producing high-quality single crystals. Since the discovery of FeSe superconductivity in 2008, researchers have made significant progress in crystal growth, overcoming the hurdles that initially impeded their studies. Consequently, they have successfully established the complete phase diagrams of 11 iron-based superconductors, including FeSe1-xTex, FeSe1-xSx and FeTe1-xSx. In this paper, we aim to provide a comprehensive summary of the preparation methods employed for 11 iron-based single crystals over the past decade. Specifically, we will focus on hydrothermal, chemical vapor transport (CVT), self-flux and annealing methods. Additionally, we will discuss the quality, size, and superconductivity properties exhibited by single crystals obtained through different preparation methods. By exploring these aspects, we can gain a better understanding of the advantages and limitations associated with each technique. High-quality single crystals serve as invaluable tools for advancing both the theoretical understanding and practical utilization of high-temperature superconductivity.

Excess conductivity study of (Bi,Pb)-2223 superconductor added with (Al2O3–15 wt% ZrO2) nanocomposite

The excess conductivity analysis is used to study the effects of Al2O3–15 wt% ZrO2 (AlZr) nanocomposite on the superconducting properties of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ (BiPb-2223) phase. A series of (BiPb-2223)1-x/(AlZr)x composite samples (0.0 wt% ≤ x ≤ 1 wt%) were synthesized by the conventional solid-state reaction method. The structural and morphological properties of the synthesized composites were studied using X-ray diffraction and scanning electron microscopy. Results showed that adding AlZr nanocomposite up to 0.5 wt% improves the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ phase formation. The excess conductivity analysis was carried out using Aslamazov–Larkin and Lawrence– Doniach approaches. The results indicated that the Fermi energy EF, Fermi velocity VF, and coherence length along the c axis ξc(0) decrease with increasing the AlZr nanocomposite concentration. The ξc(0) value decreases from 3.68 Å for AlZr free sample to 2.70 Å for x = 1.0 wt%. Moreover, superconducting critical parameters, including lower and upper critical magnetic fields (Bc1(0) and Bc2(0)) and critical current density (Jc(0)), were estimated by the Ginsberg-Landau theory. Obtained values indicated a remarkable enhancement in the mentioned critical parameters by adding the AlZr nanocomposite. The Jc(0) value enhances from 1.4 × 103 A/cm2 for AlZr free sample to 3.5 × 103 A/cm2 for the sample with 1.0 wt% additives, which shows that the Jc(0) is improved by about 150%. In addition, the critical magnetic fields are improved by about 80% in the sample containing 1.0 wt% AlZr compared to the AlZr-free sample. The observed improvement in the superconducting parameters is most likely attributed to the flux pinning capability and intergranular coupling enhancement.

On fractal thermodynamics of the superconducting transition and the roles of specific heat, entropy and critical magnetic field in disordered superconductors

In this study, we have introduced the concept of ``fractal temperature derivative'' motivated from recent works of Li and Ostoja-Starzewski in their analysis of nonlinear fractal dynamics in porous and anisotropic media. We have introduced various analytical forms of the critical magnetic field and we have discussed their thermodynamical properties, mainly the specific heat and entropy. These forms have been compared with the exact analytical form obtained based on the ``fractal temperature derivative'' approach. It was observed that these analytical forms hold a number of advantageous features which are practical to various types of superconductors including strongly disordered superconductors. Additional properties have been obtained and analyzed accordingly.

Strong magnetoelastic coupling in MnCoSi compounds studied in pulsed magnetic fields

The orthorhombic MnCoSi compounds have been found to present a large magnetoelastic coupling, which is regarded as the source for the magnetocaloric effect (MCE) and the magnetostrictive effect. As a result, these compounds are potential materials for caloric applications such as solid-state refrigeration. In the present study, we offer fundamental insights in the magnetoelastic coupling in these compounds based on their structural, metamagnetic, and MCE behavior. The directly measured adiabatic temperature change ($\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$) in different initial temperatures (down to 18 K) and pulsed magnetic fields (up to 40 T) presents a moderate MCE performance (the maximum $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=--3.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for a field change of 13 T), which results from the metamagnetic behavior of these compounds. Furthermore, the magnetization measurements in pulsed (and static) magnetic fields indicate that the magnetoelastic coupling is significantly enhanced for increasing fields resulting in an improved saturation magnetization. The metamagnetic transition is continuously pushed to lower temperatures in higher fields. The phase diagram constructed from the experimental transition temperatures ${T}_{t}$ and the critical magnetic fields ${\ensuremath{\mu}}_{0}{H}_{\mathrm{cr}}$ indicate that the transition is terminated below 18 K and that ferromagnetism is stabilized for fields above 22.3 T. Our results provide unique insights into the strong magnetoelastic coupling under high pulsed magnetic fields, providing guidelines for the design of giant magnetocaloric materials for future caloric applications.

Extracting quantum-geometric effects from Ginzburg-Landau theory in a multiband Hubbard model

We first apply functional-integral approach to a multiband Hubbard model near the critical pairing temperature, and derive a generic effective action that is quartic in the fluctuations of the pairing order parameter. Then we consider time-reversal-symmetric systems with uniform (i.e., at both low-momentum and low-frequency) pairing fluctuations in a unit cell, and derive the corresponding time-dependent Ginzburg-Landau (TDGL) equation. In addition to the conventional intraband contribution that depends on the derivatives of the Bloch bands, we show that the kinetic coefficients of the TDGL equation have a geometric contribution that is controlled by both the quantum-metric tensor of the underlying Bloch states and their band-resolved quantum-metric tensors. Furthermore we show that thermodynamic properties such as London penetration depth, GL coherence length, GL parameter and upper critical magnetic field have an explicit dependence on quantum geometry.

Size effect of randomly distributed pinning centers on magnetic vortices motion in type-Ⅱ superconductor

We consider the size effect of randomly distributed pinning centers on magnetic vortices motion in a mesoscopic type-Ⅱ superconductor in the present of magnetic field using the time-dependent Ginzburg-Landau (TDGL) equations. The pinning centers distributed randomly in various contents in the system are characterized by a distribution function p(r) which fixes the size and positions of them. We investigate the magnetization curves and the magnetic induction as a function of the external magnetic field along the z-axis. In addition, the density of superconducting electrons and the maximum magnetization values for various sizes of the pinning centers is considered. The size of the pinning centers obviously affects the dynamics of the magnetic vortices in the superconductor. The numerical simulations show that Magnetization values and the stable vortex configuration depend on not only content but also size of the pinning centers. The smaller size R (or w) by which the shape of them is characterized results in an increase (or decrease) of both the lower critical magnetic field H1 and the maximum magnetization value. The present work will show good results into understanding and studying the size effect of pinning centers on dynamics of the magnetic vortices in a mesoscopic type-Ⅱ superconductor.

Electrostatic control of the proximity effect in the bulk of semiconductor-superconductor hybrids

The proximity effect in semiconductor-superconductor nanowires is expected to generate an induced gap in the semiconductor. The magnitude of this induced gap, together with the semiconductor properties like spin-orbit coupling and g-factor, depends on the coupling between the materials. It is predicted that this coupling can be adjusted through the use of electric fields. We study this phenomenon in InSb/Al/Pt hybrids using nonlocal spectroscopy. We show that these hybrids can be tuned such that the semiconductor and superconductor are strongly coupled. In this case, the induced gap is similar to the superconducting gap in the Al/Pt shell and closes only at high magnetic fields. In contrast, the coupling can be suppressed which leads to a strong reduction of the induced gap and critical magnetic field. At the crossover between the strong-coupling and weak-coupling regimes, we observe the closing and reopening of the induced gap in the bulk of a nanowire. Contrary to expectations, it is not accompanied by the formation of zero-bias peaks in the local conductance spectra. As a result, this cannot be attributed conclusively to the anticipated topological phase transition and we discuss possible alternative explanations.

High magnetic field superconductivity in a two-band superconductor

We present a mechanism allowing for superconductivity at high magnetic fields, beyond the Pauli-Chandrasekhar-Clogston limit. We consider spin splitting induced by an in-plane external magnetic field in a superconductor with two relevant bands close to the Fermi level. The magnetic field therefore controls which bands are available for Cooper pair formation. The presence of interband superconducting pairing, i.e., Cooper pairs formed by electrons with different band indices, produces high-field reentrant superconducting domains, whose critical magnetic field violates the Pauli-Chandrasekhar-Clogston limit. We analyze how the interband superconducting domains are influenced by the band parameters, and show that, for a certain range of parameters, the system presents two separate superconducting regions, for low and high magnetic field.

Effect of thickness on the superconducting properties of the thin films of FeTe0.55Se0.45 deposited on YSZ substrates using Pulsed laser deposition (PLD) technique

We report the successful fabrication of thin films of thickness ∼26 nm, 59 nm, 76 nm, and 158 nm of the composition FeTe0.55Se0.45 on the (100)-oriented Yttria-stabilized zirconia (YSZ) substrate using the pulsed laser deposition (PLD) technique. The effect of thickness on the structure and superconducting properties of the thin films has been investigated. X-ray diffraction study reveals the growth of thin films along the c-axis. The temperature-dependent resistivity measurements confirm superconductivity in all the fabricated thin films, and the highest ∼ 16.2 K has been observed for the thin film of thickness ∼59 nm, which is higher than the corresponding value of the polycrystalline target sample. The superconducting parameters such as upper critical magnetic field coherence length thermally activated energy (TAE) U0, and vortex phase state have been measured by magnetotransport measurements near in the different applied magnetic fields up to 12 T. The TAE values determined from the conventional and modified thermally activated flux flow (TAFF) models are discussed and compared. A crossover from 2-dimensional (2D) vortex to 3-dimensional (3D) vortex behaviour has been observed. The vortex phase diagrams are used to observe the transition from the vortex liquid to the vortex glass state in the grown thin films. Moreover, magnetoresistance (MR) measurements show non-saturating linear magnetoresistance (LMR) in the high field region, indicating the presence of the possible topological state in the grown thin films. The values of magnetic field dependent transport critical current density, have been evaluated from the current-voltage (I-V) curves. Furthermore, the normalised pinning force density has been used to characterize the pinning processes using the Dew Hughes’ scaling rule which reveals that the grown thin films contain δl-surface pinning centers.

Ginzburg–Landau surface energy of multiband superconductors: derivation and application to selected systems

We determine the energy of an interface between a multiband superconducting and a normal half-space, in presence of an applied magnetic field, based on a multiband Ginzburg–Landau (GL) approach. We obtain that the multiband surface energy is fully determined by the critical temperature, electronic densities of states, and superconducting gap functions associated with the different band condensates. This furthermore yields an expression for the thermodynamic critical magnetic field, in presence of an arbitrary number of contributing bands. Subsequently, we investigate the sign of the surface energy as a function of material parameters, through numerical solution of the GL equations. Here, we consider two distinct cases: (i) standard multiband superconductors with attractive interactions, and (ii) a three-band superconductor with a chiral ground state with phase frustration, arising from repulsive interband interactions. Furthermore, we apply this approach to several prime examples of multiband superconductors, such as metallic hydrogen and MgB2, based on microscopic parameters obtained from first-principles calculations.

Large room-temperature magnetodielectric effect in polyvinylidene fluoride-trifluoroethylene/La0.7Sr0.3MnO[formula omitted] (0-3) nanocomposite thin films

We observe large room-temperature magnetodielectric effect (nearly 12% suppression of dielectric constant under ∼20 kOe field) as well as its remarkable field-driven switch – from positive to negative – in polyvinylidene fluoride-trifluoroethylene/La0.7Sr0.3MnO3 (PVDF-TrFE/LSMO) thin films (0–3 connectivity) containing 7.5 volume% LSMO. The magnetodielectric effect is mapped with the volume fraction of the LSMO nanoparticle across 5-20 volume%. It reveals a close correlation among the LSMO nanoparticles volume fraction, their distribution pattern within the PVDF-TrFE matrix, uniformity in the magnetic domain size (imaged by magnetic force microscopy), and the magnetodielectric effect. The observed 20% jump in the intrinsic bulk capacitance at a critical magnetic field HC∼10 kOe can be exploited to develop smart nanoscale magnetoelectric devices.

A flux-tunable YBa2Cu3O7 quantum interference microwave circuit

Josephson microwave circuits are essential for the currently flourishing research on superconducting technologies, such as quantum computation, quantum sensing, and microwave signal processing. To increase the possible parameter space for device operation with respect to the current standards, many materials for superconducting circuits are under active investigation. Here, we present the realization of a frequency-tunable, weakly nonlinear Josephson microwave circuit made of the high-temperature cuprate superconductor YBa2Cu3O7 (YBCO), a material with a high critical temperature and a very high critical magnetic field. An in situ frequency-tunability of ∼300 MHz is achieved by integrating a superconducting quantum interference device (SQUID) into the circuit based on Josephson junctions directly written with a helium ion microscope (HIM). Our results demonstrate that YBCO-HIM-SQUID microwave resonators are promising candidates for quantum sensing and microwave technology applications.

THE THIRD CRITICAL FIELD (HC3) OF SINGLE-CRYSTALLINE K0.73Fe1.68Se2 BY GINZBURG-LANDAU APPROACH

In this paper, two-band Ginzburg-Landau (GL) equations for magnetic superconductors were solved analytically to determine the temperature dependence of surface critical magnetic field (Hc3). By variation method analytically from 1st GL equations and modified to the Changjan & Udomsamuthirun’s temperature dependence model. We found that, our model could find a good agreement with the experimental data of single-crystalline K0.73Fe1.68Se2 superconductors vicinity the critical temperature scenery and the ratio Hc3/Hc2 (where Hc2 is the upper critical field of single-crystalline K0.73Fe1.68Se2) indicated powerful temperature dependence.

High-temperature superconductivity up to 223K in the Al stabilized metastable hexagonal lanthanum superhydride.

As compressed hydrides constantly refresh the records of superconducting critical temperatures (Tc) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P63/mmc-LaH10) stabilized at 146GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with Tc ∼ 178K, and this value is enhanced to a maximum Tc ∼ 223K at 164GPa. A huge upper critical magnetic field value Hc2(0) reaches 223 T at 146GPa. The small volume expansion of P63/mmc-(La, Al) H10 compared with the binary LaH10 indicates the possible interstitial sites of Al atoms filling into the La-H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system.

Magnetic and Magnetotransport Properties of the Magnetic Topological Nodal‐Line Semimetal TbSbTe

AbstractThe magnetic properties, magneto‐resistivity, Hall resistivity, Seebeck coefficient, and heat capacity are investigated for a magnetic topological nodal‐line semimetal TbSbTe. The calculated energy‐band structures of TbSbTe show two nodal rings on the kx‐ky planes, and the Fermi surface possesses one electron pocket with an enclosure of one hole pocket around the Γ point. The multiple magnetic phase transitions are induced at critical magnetic fields of Hc1 ≈ 10.5 kOe, Hc2 ≈ 20.8 kOe, and Hc3 ≈ 38.2 kOe at 2 K for the H // ab plane. Temperature dependence of electrical resistivity displays a hump‐like feature around 240 K, a general positive slope above TN = 6 K but a negative slope below TN. The magnetoresistance exhibits a conversion from the semi‐classical H2 dependence at weak fields to the linear‐field dependence at high fields, indicating the presence of a Dirac linear energy dispersion. TbSbTe may provide an ideal platform for studying topological physics and designing devices based on topological quantum materials.

Synthesis of an aqueous, air-stable, superconducting 1T'-WS2 monolayer ink.

Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) materials for a wide range of applications. However, many 2D materials with potential applications in quantum technologies often fail to leave the laboratory setting because of their air sensitivity and depreciation of physical performance after chemical processing. We report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T'-WS2 monolayers that are isostructural to the air-sensitive topological insulator 1T'-WTe2. The printed film is metallic at room temperature and superconducting below 7.3 kelvin, shows strong anisotropic unconventional superconducting behavior with an in-plane and out-of-plane upper critical magnetic field of 30.1 and 5.3tesla, and is stable at ambient conditions for at least 30 days. Our results show that chemical processing can make nontrivial 2D materials that were formerly only studied in laboratories commercially accessible.

A Study of the Temperature-Dependent Surface and Upper Critical Magnetic Fields in KFeSe and LaSrCuO Superconductors

The critical magnetic field is one of the most interesting properties of superconductors. Thus, this study aimed to investigate the surface and upper critical magnetic fields of superconductors in Fe-based and cuprate superconductors as KFeSe and LaSrCuO superconductors, respectively. The anisotropic two-band Ginzburg–Landau method was used to generate the analytic equation. The analytics were shown for the simplified equation so that a second-order polynomial temperature-dependent equation could be applied and fitted to the experimental results of KFeSe and LaSrCuO superconductors. After that, numerical calculations were applied to find the shape of the Fermi surface, which is an important component within the band structure. It was found that the anisotropy of the Fermi surface for each band structure was affected by the upper critical magnetic field and the surface critical magnetic field to the upper critical magnetic field of the superconductors. The second-order polynomial temperature-dependent model can be applied to other superconductors to predict the surface and upper critical magnetic fields.