Point-contact spectroscopy measurements of binary superconductor MgB2

We studied the superconductor MgB2 by point-contact spectroscopy. The first derivative conductance of the current (I)-voltage (V) characteristics dI/dV(V) displays the Andreev reflection features at the superconductor-normal metal interface. The largest gap values are estimated to be Δ(4.2 K) = 9-12 meV. We also observed clear evidences for the multiple-gaps feature with the small gap Δ(4.2 K) = 1-3 meV. These gap values agree with the previous break-junction data. The observed peak positions in the second derivative conductance (d2I/dV2(V)) are consistent with the phonon density of states of inelastic neutron scattering measurements.