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TT: Fachverband Tiefe Temperaturen
TT 50: German-French Focus Session: Superconducting Junctions and Quantum Circuits
TT 50.8: Vortrag
Mittwoch, 11. März 2026, 18:15–18:30, HSZ/0003
From Shapiro steps to photon-assisted tunneling in microwave-driven atomic-scale Josephson junctions with a single (magnetic) adatom — •Martina Trahms1,2, Bharti Mahendru1, Clemens B. Winkelmann2, and Katharina J. Franke1,3 — 1Fachbereich Physik, Freie Universität Berlin, Berlin, Germany — 2Univ. Grenoble Alpes/CEA/Grenoble-INP/IRIG-Pheliqs, Grenoble, France — 3Fachbereich Physik and Halle-Berlin-Regensburg Cluster of Excellence CCE, Freie Universität Berlin, Berlin, Germany
Understanding Josephson junctions (JJs) on the atomic scale yields insights for the prospect of superconducting circuits in future technological applications. We form JJs between a superconducting tip and sample in a scanning tunneling microscope (STM). The phase dynamics of the JJ such as dissipation and coherence of the tunneling processes are investigated by high-frequency (HF) irradiation. Shapiro steps indicate coherent Cooper-pair tunneling while incoherent tunneling processes are described by photon-assisted tunneling. With increasing HF irradiation amplitude, the STM JJs transition from the coherent to the incoherent tunneling regime due to the increase of thermal fluctuations. Introducing a magnetic adatom into the junction reduces the Josephson coupling and increases the quasiparticle tunneling rate which leads to a suppression of coherence. We highlight the presence of phase coherence in atomic scale JJs and ascribe the transition from coherent to incoherent Cooper-pair tunneling processes to the interplay of thermal fluctuations and the Josephson coupling strength.
Keywords: Josephson spectroscopy; Shapiro steps; Photon-assisted tunneling; Scanning tunneling spectroscopy