The critical Josephson currents in MgB<inf>2</inf>/normal metal/MgB<inf>2</inf>tunnel junctions: Bogoliubov-de Gennes approach

Abstract

The Josephson currents passing through the S1/N/S2double tunnel junctions where S1can be either an MgB2or a conventional superconductor (CS), S2is MgB2and N is a normal metal are investigated. The Bogoliubov-de Gennes approach is used to calculate the Andreev reflection coefficients at the S1/N interface barrier. The Fermi wave vectors mismatch among S1, N and S2, and the difference in the TC's of the two superconductors are taken into account. For the MgB2/N/MgB2junction, the Josephson currents in both the c-axis and the ab-plane orientation alignments are studied. For the CS/N/MgB2junctions, only the Josephson current in the c-axis orientation is studied. Our results for critical Josephson currents flowing along c-axis orientation of both types of S1/N/S2junctions are compared to four sets of the experimental data. We find that the fitting of the experimental data for the temperature dependence of the Josephson junctions to our results are in good agreement in all four cases. © 2007 Elsevier B.V. All rights reserved.