Impact of Atomic-Scale Contact Geometry on Andreev Reflection.
Charge transport has been examined in junctions comprising the normal-metal tip of a low-temperature scanning tunneling microscope, the surface of a conventional superconductor, and adsorbed C_{60} molecules. The Bardeen-Cooper-Schrieffer energy gap gradually evolves into a zero-bias peak with decreasing electrode separation. The peak is assigned to the spectroscopic signature of Andreev reflection. The conductance due to Andreev reflection is determined by the atomic termination of the tip apex and the molecular adsorption orientation. Transport calculations unveil the finite temperature and the strong molecule-electrode hybridization as the origin to the surprisingly good agreement between spectroscopic data and the Blonder-Tinkham-Klapwijk model that was conceived for macroscopic point contacts.
Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany.
J
J
Brand
CeFEMA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
P
P
Ribeiro
Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany.
N
N
Néel
Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058, China.
S
S
Kirchner
Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany.
J
J
Kröger