Point-contact spectroscopy of magnesium diboride with different counter-electrodes

2004/01/23 by A. I. D'yachenko, V. Yu. Tarenkov, M. A. Belogolovskii +3
Physics and Astronomy · #cond-mat.supr-con

paper · pdf · doi:10.1142/s0217984903006505

published as Mod. Phys. Lett. B 17, 1405 (2003) · 12 pages, 4 figures

arxiv created 2004/01/23 · arxiv updated 2009/12/01

Abstract

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 a rounded contribution of the larger gap. Junctions with a superconducting lead counter-electrode pressed into a bulk MgB2 sample reveal two conductance peaks that are interpreted as the result of the formation of highly-transmitting break junctions inside the magnesium diboride ceramic. Our results strongly support the two-band model with two different gap values on quasi-two-dimensional σ(7.1 meV) and three-dimensional π(2.7 meV) Fermi surface sheets of MgB2.

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