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TT: Fachverband Tiefe Temperaturen

TT 11: Superconductivity: Poster

TT 11.21: Poster

Montag, 17. März 2025, 15:00–18:00, P4

Control of Andreev Reflection via a Single-Molecule Orbital — •Lorenz Meyer¹, Jose L. Lado², Nicolas Néel¹, and Jörg Kröger¹ — ¹Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany — ²Department of Applied Physics, Aalto University, 02150 Espoo, Finland

Charge transport across a single-molecule junction fabricated from a normal-metal tip, a phthalocyanine, and a conventional superconductor in a scanning tunneling microscope is explored as a function of the gradually closed vacuum gap. The phthalocyanine (2H-Pc) molecule and its pyrrolic-hydrogen-abstracted derivative (Pc) exhibit vastly different behavior. Andreev reflection across the 2H-Pc contact exhibits a temporary enhancement that diminishes with increasing conductance. The hybridization of 2H-Pc with the tip at contact formation gives rise to a molecular magnetic moment that is Kondo-screened in the tip. In contrast, the single-Pc junction lacks Andreev reflection in the same conductance range. Spectroscopy experiments and supporting nonequilibrium Green function calculations highlight the importance of a molecular orbital close to the Fermi energy for rationalizing the observations.

Funding by the DFG through KR 2912/18-1 and KR 2912/21-1 is acknowledged.

Keywords: Andreev Reflection; Single-Molecule Contact; Scanning Tunneling Microscopy