Minimal model of point contact Andreev reflection spectroscopy of multiband superconductors

We formulate a minimal model of point contact Andreev reflection spectroscopy of a normal-metal/multiband superconductor interface. The theory generalizes the Blonder-Tinkham-Klapwijk formulation to a multiband superconductor and it is based on the quantum waveguide theory. The proposed approach allows an analytic evaluation of the Andreev and normal reflection coefficients and thus is suitable for a data fitting of point contact experiments. The obtained differential conductance curves present distinctive features similar to those measured in the experiments on multiband superconductors, such as iron-based pnictides and MgB2.