Search

Featured Application: This work concerns the study of the granular nature of an YBa2Cu3O7-x superconducting film, whose expertise can be useful in understanding the temperature and the DC and AC field application ranges of these materials with non-optimized fabrication properties, which are typically found in superconducting wires and power cables. The study of granularity in superconducting films by using AC susceptibility has a crucial role in the development of and improvement in the ReBCO-coated conductors, which are a constantly evolving reality in the modern power applications of superconductivity. Specifically, the study of the granularity is essential because the ReBCO superconducting wires and tapes are far from the regularity of a single crystal while they often present an inter- and intragranular contribution to the critical current density. On the other hand, the AC susceptibility is a key part of the characterization of a granular sample because this technique is very sensitive to the presence of granularity in the superconductors and, moreover, the study of its first harmonic allows for determining pivotal properties such as the pinning energy as well as the dissipation processes acting in the sample. The pinning energy values and the granularity of an YBCO thin film have been studied by means of AC susceptibility measurements as a function of the AC amplitude, temperature, and DC field. In particular, the first harmonic imaginary component of the AC susceptibility χ 1 ″ related to the dissipation processes of the sample has been studied. First, starting from the Brandt approach, the critical current density Jc and the pinning energy U of the sample have been extracted at 77 K by using the χ 1 ″ measurements as a function of the AC amplitude at different AC frequencies and DC fields. From these measurements, a first signal of granularity appears. In order to confirm it, the temperature dependence of the χ 1 ″ at different DC fields has been studied and a contribution deriving from the inter- and intragranular part of the sample has emerged. By taking the temperature corresponding to the crossover between the two contributions at the different DC fields, the intergranular and intragranular response has been separated. Successively, the temperature has been fixed to 77 K, together with an AC frequency equal to 1597.9 Hz, and the χ 1 ″ as a function of the DC field at different AC amplitudes has been analyzed showing a clear presence of granularity in all the curves. By drawing the contour plot of the χ 1 ″ with the DC and AC values, it was possible to determine the best parameters to put at 77 K in order to exploit the material for applications. [ABSTRACT FROM AUTHOR]

The multifaceted inductive technique of AC magnetic susceptibility (ACMS) provides versatile and reliable means for the investigation of the respective properties of magnetic and superconducting materials. Here, we explore, both mathematically and experimentally, the ACMS set-up, based on four coaxial pick-up coils assembled in the second-derivative configuration, when employed in the investigation of differently shaped superconducting specimens of poly-crystalline YBa2Cu3O7−δ and Bi2−xPbxSr2Ca2Cu3O10+y and single-crystalline YBa2Cu3O7−δ. Through the mathematical modeling of both the ACMS set-up and of linearly responding superconducting specimens, we obtain a closed-form relation for the DC voltage output signal. The latter is translated directly to the so-called extrinsic ACMS of the studied specimen. By taking into account the specific characteristics of the studied high-Tc specimens (such as the shape and dimensions for the demagnetizing effect, porosity for the estimation of the superconducting volume fraction, etc.), we eventually draw the truly intrinsic ACMS of the parent material. Importantly, this is carried out without the need for any calibration specimen. The comparison of the mathematical modeling with the experimental data of the aforementioned superconducting specimens evidences fair agreement. [ABSTRACT FROM AUTHOR]

Some times ago, in the framework of the Boltzmann kinetic equation in the so-called τ -approximation, it was shown that perpendicular resistivity in quasi-two-dimensional (Q2D) conductors can be impurity independent in a broad range of high parallel magnetic fields [A. G. Lebed and N. N. Bagmet, Phys. Rev. B 55 (1997) R8654]. In this paper, we demonstrate that this result is much more general than the Boltzmann kinetic equation in the τ -approximation and is valid in a pure Q2D metal at low frequencies of the electric field. The above-mentioned statement open possibilities to test the above discussed phenomenon in a number of Q2D organic, high-Tc, and some other Q2D superconductors in their metallic phases and gives a method to extract some important information about their Q2D Fermi surfaces. [ABSTRACT FROM AUTHOR]

Self-repair, as a natural phenomenon, has been vastly observed and investigated in a variety of fields. With such an ability, living species self-heal their wounds to restore physiological functions while non-biological materials return to their original states, for example, thin surface layer growth occurs in the regeneration of incomplete KH2PO4 crystals. Here, two seeding strategies are developed for creating incomplete crystallographic shapes (i.e. right-angled concave corners) of YBa2Cu3O7−δ (YBCO) superconducting crystals with self-repairing capability in top-seeded melt growth. One involves in situ self-assembly seeding, by which the ability to self-repair promotes YBCO growth; the other is vertically connected seeding, by which self-repair triggers YBCO nucleation. Consequently, rapid surface crystallization originated at concave corners and swiftly generated initial growth morphology approaching equilibrium. Furthermore, these rapid-growth regions including the concave crystal or seed innately functioned as sizable effective seeding regions, enabling the enlargement of the c-oriented growth sector and the enhancement of properties for YBCO crystals. This work demonstrates experimentally that biaxial-in-plane-aligned crystals and precisely perpendicular-arranged seeds are important self-repairing activators for the rapid growth of YBCO crystals. This nature-inspired self-repairing work offers insights into the design of seeding architecture with non-equilibrium morphology for inducing sizable high-performance crystals in the YBCO family and other functional materials.

The temperature dependences of both fluctuation conductivity (FLC) σ′(T) and pseudogap (PG) Δ*(T) derived from measurements of resistivity ρ(T) of an optimally doped YBa2Cu3O7−δ single crystal subjected to long-term storage have been studied. The as-grown sample S1 exhibits characteristics typical of optimally doped YBa2Cu3O7−δ single crystals containing twins and twin boundaries. Analysis of both FLC and PG showed an unexpected improvement in all characteristics of the sample after 6 years of storage (sample S2), indicating that the effect of twin boundaries is somehow limited. After 17 years of storage, all characteristics of the sample changed dramatically, which indicates a strong influence of internal defects formed during the aging process. For the first time, the temperature dependences of both FLC and PG were obtained after 17 years of storage. [ABSTRACT FROM AUTHOR]

The origin of the high-temperature superconductivity of cuprates remains a subject of debate after almost four decades of investigation. One of the main questions — what is the physics behind the mechanism of superconducting pairing, which makes it possible to obtain real Cooper pairs at temperatures much higher than 100 K, remains open. It is believed that the answer can be obtained by the studying the properties of cuprates in the normal state above Tc, where the pseudogap (PG) opens at T* >> Tc. The number of papers devoted to the study of PG is extraordinarily large, but its physics also remains in question. In cuprates, the question arises whether the pseudogap phase arises exclusively due to antiferromagnetic fluctuations, spin or charge density waves, or whether it can be explained by the formation below T* of specific paired fermions, the so-called local pairs. We review studies on both approaches to PG that should clarify this issue. In addition to theoretical considerations, we analyze and discuss various experimental results of fluctuation conductivity and PG measurements, as well as magnetic measurements, in an attempt to prove the decisive role of local pairs in the formation of the PG state. Accordingly, various types of supposed magnetic interactions can be considered as possible mechanisms of superconducting pairing in high-temperature superconductors. [ABSTRACT FROM AUTHOR]

We have investigated the effect of Niobium and Nano CuO (40 nm) dopingY1-xNbxBa2Cu3O7-∂ compounds with 0.00 ≤ x ≤ 0.05 wt. %, prepared by the conventional solid-state method by means of XRD, SEM, R(T) and magnetic loops (M-H) measurements. The critical current densities, Jc as a function of temperature have been calculated using the critical state model from the hysteresis loops up to 1 kG at the temperature range of 10-60 K. Magnetic flux pinning, Fp of samples was calculated by using Lorentz force. The temperature dependence of the electrical resistivity measurement curves indicated that the sample with x=0.01 wt.% has a high transition temperature, Tc. XRD analysis shows a shorter c axis lattice parameter and higher orthoromthcity than the pure Y-123 and other Nb-doped samples. It was also found from Jc and Fp measurement, that the 0.01 wt.% Nb substation for the Y on YBCO superconductor improves the Jc and Fp.

We have studied the effect of sol–gel synthesis conditions on the structural and magnetic properties of the high-Tc superconductor YBa2Cu3Oy (y = 6.92 ± 0.02). Two low-temperature (<800°C) synthesis procedures have been used, differing in the annealing sequence and atmosphere (argon or oxygen). In one procedure, the starting mixture was annealed in an oxygen atmosphere, and the resultant nonsuperconducting tetragonal phase (X-phase) was heat-treated further. In the other procedure, synthesis was carried out in an argon atmosphere, which allowed a superconducting orthorhombic phase to be obtained even after the first anneal. At the same time, it is the former synthesis procedure which has made it possible to obtain nanoparticles and prepare a series of samples with a gradually decreasing degree of structural disorder owing to sequential two-step anneals (argon + oxygen). This approach helps understand general behavior of the structural characteristics, magnetic properties, and superconducting parameters of YBa2Cu3Oy high-Tc materials differing in the degree of structural disorder. [ABSTRACT FROM AUTHOR]

In this paper optical absorption of high-Tc superconductors in the infrared region is investigated within the framework of the spin polaron theory. The approach uses a representation where holes are spinless fermions while spins are normal bosons. Thus, we explored infrared absorption in high-Tc superconductors at finite temperature in a completely analytical way. This task is done through the use of the Matsubara Green's function method in the spin polaron formulation. Infrared absorption is then analyzed in terms of the conductivity which is a function of the energy gap and the frequency of the infrared energy. Our main result is consistent with the conductivity of superconductors in the clean limit. [ABSTRACT FROM AUTHOR]

We have investigated the effects of lead (Pb) additions (x) up to 40 wt% (x = 0–0.4) on the structure, electrical properties, and magnetic properties of FeSe0.5Te0.5 superconductor. The samples were prepared by the solid-state reaction method and were characterized by various techniques. The parent compound (x = 0) showed the onset temperature T c onset of 15 K, and zero-resistance temperature, T c offset of 12 K. The addition of Pb enhances the metallic characteristics of FeSe0.5Te0.5, but both T c onset and T c offset are decreased to the lower temperature with the broadened transition width. The T c onset is nearly the same (10.3 K) at higher additions, such as x = 0.3 and 0.4, but zero resistivity is not observed up to 7 K. Microstructural analysis and transport studies suggest that for x > 0.05, Pb additions weakened the coupling between grains and suppressed the superconducting percolation, leading to a broad transition. More importantly, the inclusion of a relatively small amount of Pb (x = 0.05) increased the critical current density, Jc, in the entire magnetic field, which might be attributed to better phase uniformity as well as good grain connectivity. [ABSTRACT FROM AUTHOR]

We have investigated the effects of lead (Pb) additions (x) up to 40 wt% (x = 0–0.4) on the structure, electrical properties, and magnetic properties of FeSe0.5Te0.5 superconductor. The samples were prepared by the solid-state reaction method and were characterized by various techniques. The parent compound (x = 0) showed the onset temperature T c onset of 15 K, and zero-resistance temperature, T c offset of 12 K. The addition of Pb enhances the metallic characteristics of FeSe0.5Te0.5, but both T c onset and T c offset are decreased to the lower temperature with the broadened transition width. The T c onset is nearly the same (10.3 K) at higher additions, such as x = 0.3 and 0.4, but zero resistivity is not observed up to 7 K. Microstructural analysis and transport studies suggest that for x > 0.05, Pb additions weakened the coupling between grains and suppressed the superconducting percolation, leading to a broad transition. More importantly, the inclusion of a relatively small amount of Pb (x = 0.05) increased the critical current density, Jc, in the entire magnetic field, which might be attributed to better phase uniformity as well as good grain connectivity. [ABSTRACT FROM AUTHOR]

Does a supercurrent drag space-time or generate a gravitational field that can be measured in a laboratory environment? A number of theories suggest that space-time itself could be modeled as a superfluid, so a current of Cooper-pairs might couple to its surroundings differently compared to non-quantum matter. On the other hand, experiments appeared in the literature suggesting that a discharge through a high-Tc superconductor generates a force beam, which can be picked up by external sensors. We developed a unique facility to investigate if such a link exists with unprecedented accuracy. Instead of measuring with sensors far away from the superconductor, we built a very precise thrust balance that features a cryostat allowing to measure any anomalous force directly from the superconducting source. An onboard battery and a wireless-controllable power supply as well as strict coaxial current leads ensure that any magnetic interaction with its surroundings is below the measurement noise. Our tests were done for both BSCCO and YBCO superconductors with and without the presence of a magnetic field parallel to the current flow. No force was seen within our resolution of around 100 nN for currents up to 15 A. This puts strong limits on all proposed theories and experimental claims.

We perform variational Monte Carlo simulations of the single-band Hubbard model on the square lattice with both nearest ( t ) and next-nearest ( t ') neighbor hoppings. Our work investigates the consequences of increasing hole doping on the instauration of stripes and the behavior of the superconducting order parameter, with a discussion on how the two phenomena affect each other. We consider two different values of the next-nearest neighbor hopping parameter, that are appropriate for describing cuprate superconductors. We observe that stripes are the optimal state in a wide doping range; the stripe wavelength reduces at increasing doping, until stripes melt into a uniform state for large values of doping. Superconducting pair-pair correlations, indicating the presence of superconductivity, are always suppressed in the presence of stripes. Our results suggest that the phase diagram for the single-band Hubbard model is dominated by stripes, with superconductivity being possible only in a narrow doping range between striped states and a nonsuperconducting metal., (Creative Commons Attribution license.)

In this work, I shall summarize different phenomenological approaches of vortex trapping as well in conventional superconductors that serve as a basis for experimental fact interpretations in new superconductors as in massive and nanometric high critical temperature superconductors, and I shall present our experimental studies on vortex trapping in single crystals of La1.85Sr0.15CuO and YBa2Cu3O7-δ but also in nanoparticles of YBa2Cu3O7-δ. Particular attention should be paid to the study of high-TC superconducting nanoparticles of YBa2Cu3O7-δ system doped with magnetic nanoparticles of Y3Fe5O12. The reduction in the size of grains of these two compounds by mechanical grinding led to the size disparities of these grains, confirmed by an analysis by means of an atomic force microscope. These disparities are inherent in mechanical grinding. The average sizes of the obtained nanoparticles were estimated to be in the range of 80 nm by means of XRD reflection using the Scherrer equation. The nanometric size of the obtained grains revealed new phenomena considered in the past as contradictory like the coexistence of ferromagnetism and superconductivity and the trapping of vortices by spins which were studied here in detail and allowed us highlighting this coexistence and interpreting the variations in field and temperature of the critical current density JC in this system. [ABSTRACT FROM AUTHOR]

The 2019 discovery of high temperature superconductivity in layered nickelate films, Nd1-xSrNiO2, has galvanized a community that has been studying nickelates for more than 30 years both as cuprate analogs and in their own right. On the surface, infinite layer nickelates, and their multilayer analogs, should be promising candidates based on our understanding of cuprates: square planar coordination and a parent d9 configuration that places a single hole in a dx2-y2 planar orbital makes nickelates seem poised for superconductivity. But creating crystals and films of sufficient quality of this d9 configuration in Ni1+ has proven to be a synthetic challenge, only recently overcome. These crystalline specimens are opening windows that shed new light on the cuprate-nickelate analogy and reveal nuances that leave the relationship between cuprates and nickelates very much an area open to debate. This Perspective gives a qualitative, phenomenological account of these newly discovered superconductors and multilayer members of the infinite layer nickelate family. The focus is on our current understanding of electronic and magnetic properties of these materials as well as some future opportunities, explored from the viewpoint of synthetic challenges and some suggested developments in materials discovery and growth to make further progress in this rejuvenated field.

[Display omitted] • A 0.53 nm thick CuO interlayer is observed between the Bi-2201 film and the MgO substrate. • The Bi-2201 film is subjected to in-plane residual compressive strain (−0.573%). • The reason for the inversion of the strain state is the thermal expansion mismatch. Due to the crucial influence of interface structure and strain on the performance of heterojunctions, they have received extensive attention in recent years. In this article, the interface structure and strain of the Bi 2 Sr 2 CuO 6+δ d (Bi-2201)/MgO superconducting heterojunction prepared by molecular beam epitaxy were investigated by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDX), and geometric phase analysis (GPA). The interfacial atomic sequence is determined as MgO-(CuO-CuO-Cu/BiO)-(Bi-2201) n , where a 0.53 nm thick CuO interlayer accompanied by Bi/Cu atomic co-occupation is observed between the Bi-2201 film and the MgO substrate. In addition, there is a typical coherent lattice-matching epitaxial interface between CuO/MgO with no defects and a semi-coherent domain-matching epitaxial interface between Bi-2201/CuO accompanied by an ideal misfit dislocation network. Because misfit dislocations almost compensate for the strain caused by lattice mismatch, the final Bi-2201 film undergoes in-plane compressive strain (ε xx ~ −0.573%) rather than expected tensile strain relative to bulk Bi-2201, which is attributed to the thermal expansion mismatch. The compressive strain gradually releases as the distance from the heterointerface increases. [ABSTRACT FROM AUTHOR]