2005/08/31 by Filippo Giubileo, Marco Aprili, M. Aprili +6
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity in MgB2 and Alloys #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.72.174518
published as Phys. Rev. B 72, 174518 (2005) · 8 pages, 5 figures. Replaced with published version
openalex publication_date 2005/11/23 · arxiv created 2006/01/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
Superconducting microconstrictions between Nb tips and high-quality MgB2 pellets have been realized by means of a point-contact inset, driven by a micrometric screw. Measurements of the current-voltage characteristics and of the dynamical conductance versus bias have been performed in the temperature range between 4.2\phantom\rule0.3em0exK and 500\phantom\rule0.3em0exK. Above the Nb critical temperature TCNb, the conductance of the MgB2/normal-metal constrictions behaves as predicted by the Blonder-Tinkham-Klapwijk model for low-resistance contacts while high-resistance junctions show quasiparticle tunneling characteristics. Consistently, from the whole set of data we infer the value \ensuremathΔ_\ensuremathπ=2.5\ifmmode±\else\textpm\fi0.2\phantom\rule0.3em0exmeV for the three-dimensional (3D) gap of MgB2. Below TCNb, low-resistance contacts show Josephson current and subharmonic gap structures, due to multiple Andreev reflections. Simultaneous observations of both features unambiguously indicate a coupling of the 3D band of MgB2 with the Nb superconducting order parameter. We found that the temperature dependence of the Josephson critical current follows the classical Ambegaokar-Baratoff behavior with a value ICRN=(2.1\ifmmode±\else\textpm\fi0.1)\phantom\rule0.3em0exmeV at low temperatures.