Transport through superconducting junctions proceeds via single electrons, Cooper pairs or even larger number of electrons, depending on bias voltage and tunnel coupling strength. It has been suggested that photon-assisted tunneling can be used as a tool to determine the number of charge carriers in a single tunneling event. Here, we study the transport processes through superconducting junctions, which include individual magnetic adatoms. These induce additional resonances inside the superconducting energy gap. Using photon-assisted tunneling in a scanning tunneling microscope, we reveal two distinct regimes of charge transport. At low tunnel coupling the current is carried by single electrons, while at large tunnel coupling resonant Andreev reflections dominate the transport processes.
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QuCoLiMaTalks are the weekly seminar of the collaborative research center TRR 306 QuCoLiMa (Quantum Cooperativity of Light and Matter). The talks are given by (external) experts, whose research falls within the scope of QuCoLiMa.