High current-carrying capability in c-axis-oriented superconducting MgB2 thin films

High critical current density and high-tolerance superconductivity in high-entropy alloy thin films

High-entropy alloy (HEA) superconductors—a new class of functional materials—can be utilized stably under extreme conditions, such as in space environments, owing to their high mechanical hardness and excellent irradiation tolerance. However, the feasibility of practical applications of HEA superconductors has not yet been demonstrated because the critical current density (J_c) for HEA superconductors has not yet been adequately characterized. Here, we report the fabrication of high-quality superconducting (SC) thin films of Ta–Nb–Hf–Zr–Ti HEAs via a pulsed laser deposition. The thin films exhibit a large J_c of >1 MA cm⁻² at 4.2 K and are therefore favorable for SC devices as well as large-scale applications. In addition, they show extremely robust superconductivity to irradiation-induced disorder controlled by the dose of Kr-ion irradiation. The superconductivity of the HEA films is more than 1000 times more resistant to displacement damage than that of other promising superconductors with technological applications, such as MgB₂, Nb₃Sn, Fe-based superconductors, and high-T_c cuprate superconductors. These results demonstrate that HEA superconductors have considerable potential for use under extreme conditions, such as in aerospace applications, nuclear fusion reactors, and high-field SC magnets.

Thin-film high-entropy alloy (HEA) superconductors have recently attracted a lot of attention, but their critical current density and potential usefulness in engineering applications has remained unclear. Here, the authors fabricate HEA films with remarkably high critical current density and resistance to radiation damage.

Influence of pressure on the transport, magnetic, and structural properties of superconducting Cr0.0009NbSe2 single crystal

We investigate the superconducting critical current density (J _c), transition temperature (T _c), and flux pinning properties under hydrostatic pressure (P) for Cr_0.0009NbSe₂ single crystal. The application of P enhances T _c in both electrical resistivity (∼0.38 K GPa^-1: 0 ≤ P ≤ 2.5 GPa) and magnetization (∼0.98 K GPa^-1: 0 ≤ P ≤ 1 GPa) measurements, which leads to a monotonic increase in J _c and flux pinning properties. The field-dependent J _c at various temperatures under P is analyzed within the collecting pinning theory and it shows that δT _c pinning is the crossover to δl pinning above the critical pressure (P _c ∼0.3 GPa). Our systematic analysis of the flux pinning mechanism indicates that both the density of pinning centers and pinning forces greatly increase with the application of P, which leads to an enhancement in the vortex state. Structural studies using synchrotron X-ray diffraction under pressure illustrate a stable hexagonal phase without any significant impurity phase and lattice parameter reduction with P shows highly anisotropic nature.

Enhancement of the critical current density in FeO-coated MgB(2) thin films at high magnetic fields

The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB(2) thin films on the critical current density was studied in comparison with the case of uncoated MgB(2) thin films. We calculated the superconducting critical current densities (J(c)) from the magnetization hysteresis (M-H) curves for both sets of samples and found that the J(c) value of FeO-coated films is higher at all fields and temperatures than the J(c) value for uncoated films, and that it decreases to ~10(5) A/cm(2) at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T.

In situ epitaxial MgB2 thin films for superconducting electronics

The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2.