Interband Pairing Interaction in Magnesium Diboride Probed by Tunneling Spectroscopy
We report on the study of the interband pairing interaction in the two-band superconductor MgB2 by tunneling spectroscopy using thin film tunnel junctions. The films were deposited in situ by an approach comprising a conventional planar B sputter gun and a special homemade Mg evaporator providing a high vapor pressure. For the tunneling experiments sandwich-type crossed-strip tunnel junctions with a native MgB2 oxide as the potential barrier and Al, In or Pb counterelectrodes were prepared. Voltage-dependent differential conductance measurements revealed estimates of the barrier thickness and height of 1.5 nm and 1.6 eV, respectively, and allowed us to determine the phonon-induced structures in the tunneling density of states of the phonon-mediated superconductor MgB2. The analysis of the reduced density of states using the standard single-band Eliashberg equations yielded an effective electron-phonon spectral function accounting for the smaller energy gap. A further analysis involving ab-initio LDA calculations and the two-band Eliashberg equations revealed that the dominant feature in the effective spectral function, a strong peak at 58 meV, was mainly due to the interband pairing interaction.
P. VINCENZINI and A. RIGAMONTI
R. Schneider et al., "Interband Pairing Interaction in Magnesium Diboride Probed by Tunneling Spectroscopy", Advances in Science and Technology, Vol. 47, pp. 69-74, 2006