Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging (MRI). The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demo...

We present a comparison of electron-phonon interaction in NbB2 and MgB2, calculated using full-potential, density-functional-based methods in P6/mmm crystal structure. Our results, described in terms of (i) electronic structure, (ii) phonon density of states F (ω), (iii) Eliashberg function α2F (ω), and (iv) the solutions of the isotropic Eliashberg gap equation, clearly show significant differ...

Phonon spectra have been investigated by micro-Raman scattering from 290 to 20K. New peaks at 500 and 674 cm appear below 250K in MgB2. These peaks are explained by the Fermi resonance, where Raman-active E2g intereacts with the overtone of E1u due to anhamonicity. Raman spectra of the isostructural RB2 (R=Al, Mn, Nb and Ti) have been also measured at 290K. The line width of E2g phonon of the s...

We report on tunneling and Andreev-reflection conductance spectra of 39 K superconducting magnesium diboride, obtained with Pb and Au counter-electrodes. Two distinct steps at close to 2.7 and 7.1 meV appear in a low-resistance metallic-type Au-MgB2 junction characteristic, whereas a tunneling-like spectrum measured for the same junction, annealed by the application of dc current, exhibits only...

Micrometre-sized MgB2 crystals of varying quality, synthesized at low temperature and autogenous pressure, are compared using a combination of Raman and infra-red (IR) spectroscopy. These data, which include new peak positions in both spectroscopies for high quality MgB2, are interpreted using DFT calculations on phonon behaviour for symmetry-related structures. Raman and IR activity additional...

The phases in Cu sheathed MgB2 wires fabricated using very short annealing time are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and critical current (Ic) measurements. By comparison with the XRD pattern of our synthesized MgCu2, the XRD line located at 2h 36.1 for all Cu-sheathed MgB2 wire samples is unambiguously identified to be due to the MgCu2 phase. This line wa...

For applications of MgB2 wires or tapes, high critical currents in high magnetic fields are essential. By using tapes in superconducting coils the anisotropic behaviour of the critical current, i.e. the dependence on the direction of the external field in relation to the tape surface, has to be taken into account. The anisotropy of MgB2 tapes with mechanically alloyed (MA) precursor powder and ...

In this paper, we report our extensive investigations of layered superconductors within a continuous Ginzburg–Landau model. The calculated results suggest that the parallel upper critical field generally increases with the transition temperature and may be correlated with the behaviours of the order parameters. The calculated upper critical fields of MgB2 are in reasonably good agreement with e...