2014/12/05 by A. A. Polyanskii, Anatolii Polyanskii, Fumitake Kametani +13
Materials Science · Physics and Astronomy · #Anisotropy #Condensed matter physics #Geometry #Iron-based superconductors research #Materials science #Optics #Perpendicular #Physics #Physics of Superconductivity and Magnetism #Superconductivity #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.90.214509
published as Phys. Rev. B 90, 214509 (2014) · 21 pges, 13 figures
openalex publication_date 2014/12/05 · arxiv created 2014/12/06 · arxiv updated 2014/12/10 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Investigations of MgB2 and Fe-based superconductors in recent years have revealed many unusual effects of multiband superconductivity, but manifestations of anisotropic multiband effects in the critical current density Jc have not been addressed experimentally, mostly because of the difficulties in measuring Jc along the c axis. To investigate the effect of very different intrinsic anisotropies of \ensuremathσ and \ensuremathπ electron bands in MgB2 on current transport, we grew epitaxial films with a tilted c axis (\ensuremathθ \ensuremath∼ 19.5\ifmmode^∘\else\textdegree\fi), which enabled us to measure the components of Jc along both the ab plane and the c axis using magneto-optical and transport techniques. These measurements were combined with scanning and transmission electron microscopy, which revealed terraced steps on the surface of the tilted-c-axis films. The measured field and temperature dependencies of the anisotropic Jc(H) show that Jc,L parallel to the terraced steps is higher than Jc,T perpendicular to the terraced steps, and Jc of thinner films (50 nm) obtained from transport experiments at 0.1 T reaches \ensuremath∼10% of the depairing current density Jd in the ab plane, while magneto-optical imaging revealed much higher Jc at lower fields. To analyze the experimental data we developed a model of anisotropic vortex pinning which accounts for the observed behavior of Jc in the tilted-c-axis films and suggests that the apparent anisotropy of Jc is affected by current pairbreaking effects in the weaker \ensuremathπ band. Our results indicate that the out-of-plane current transport mediated by the \ensuremathπ band could set the ultimate limit of Jc in MgB2 polycrystals.