Role of critical current on the point-contact Andreev reflection spectra between a normal metal and a superconductor

The point-contact spectrum between a normal metal and a superconductor often shows unexpected sharp dips in the conductance at voltage values larger than the superconducting energy gap. These dips are not predicted in the Blonder-Tinkham-Klapwijk (BTK) theory, commonly used to analyze these contacts. We present here a systematic study of these dips in a variety of contacts between different combinations of a superconductor and a normal metal. From the correlation between the characteristics of these dips with the contact area, we conclude that such dips are caused by the contact not being in the ballistic limit. An analysis of the possible errors introduced while analyzing such a spectrum with the standard BTK model is also presented.