Ye.S. Avotina, Yu.A. Kolesnichenko, and J.M. van Ruitenbeek, Influence of a single defect on the conductance of a tunnel point contact between a normal metal and a superconductor: Электpонные свойства металлов и сплавов, Low Temp. Phys. 34, (2008) [Fiz. Nizk. Temp. 34, 1184-1191, (2008)] DOI: https://doi.org/10.1063/1.3009591.