From tunneling to contact in a magnetic atom: The non-equilibrium Kondo effect
A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA. ; D.J.C. acknowledges the European Union for support under H2020-MSCA-IF-2014 Marie-Curie Individual Fellowship programme Proposal No. 654469. P.A. acknowledges the CCT-Rosario Computational Center. Financial support from CONICET, the Agence Nationale de la Recherche (Grant Nos. ANR-13-BS10-0016, ANR-11-LABX-0058 NIE, and ANR-10-LABX-0026 CSC), and MINECO (Grant No. MAT2015-66888-C3-2-R) is gratefully acknowledged. ; Peer Reviewed