2001/08/06 by R. Prozorov, R. W. Giannetta, S. L. Bud'ko +2 · 1 citation
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.64.180501
RevTeX 4, 4 EPS figures
arxiv created 2001/08/06 · openalex publication_date 2001/10/01 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Measurements of the penetration depth \ensuremathλ(T,H) in the presence of a dc magnetic field were performed in MgB2 wires. In as-prepared wires \ensuremathλ(T,H<130 Oe) shows a strong diamagnetic downturn below \ensuremath≈10 K. A dc magnetic field of 130 Oe completely suppressed the downturn. The data are consistent with proximity coupling to a surface Mg layer left during synthesis. A theory for the proximity effect in the clean limit, together with an assumed distribution of the Mg layer thickness, qualitatively explains the field and temperature dependence of the data. Removal of the Mg by chemical etching results in an exponential temperature dependence for \ensuremathλ(T) with an energy gap of 2\ensuremathΔ(0)/Tc\ensuremath≈1.54 [\ensuremathΔ(0)\ensuremath≈2.61 meV], in close agreement with recent measurements on commercial powders and single crystals. This minimum gap is only 44% of the BCS weak coupling value, implying substantial anisotropy.