Tunneling density of states of MgB2: evidence for a dominant π-band contribution



Weakly-transmitting junctions usable for tunneling spectroscopy experiments were fabricated from polycrystalline bulk samples of magnesium diboride with a niobium counter-electrode. A strong nonlinear conductance-versus-voltage behavior for voltages above the values corresponding to the energy gaps of the electrodes was interpreted as a fingerprint of the electron-phonon interaction in superconducting MgB2. A partial Eliashberg spectral function α2(ω)F(ω) was extracted from the data by the numeric inversion of the standard strong-coupling Eliashberg equations. In a full agreement with recent theoretical simulations for magnesium diboride [1], we have observed a dominant contribution from the π-band of this two-band superconductor. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)