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Josephson spectroscopy of single atoms in a scanning tunneling microscope

Dr. Martina Trahms (LATEQS / PHELIQS / CEA / Grenoble INP)

Abstract Josephson spectroscopy is performed in a scanning tunneling microscope (STM) on single magnetic adatoms on a Pb(111) surface by bringing the superconducting STM tip into close proximity to the surface. The magnetic moment of the atom’s unpaired electrons couples to the superconducting condensate and induces localized bound states (YSR states). The tunneling probability for electrons and holes into the YSR states is known to vary due to potential scattering on the surface (electron-hole asymmetry). In the investigated Josephson junctions, the magnetic adatoms induce non-reciprocal behavior, i.e., the transition from the resistive single-particle conductance into the Cooper-pair tunneling regime depends on the direction of the applied current. The observed non-reciprocity can be correlated to the damping properties of the Josephson junction caused by the electron-hole asymmetry of the YSR bound states. To further investigate the phase dynamics of these Josephson junctions, the influence of high frequency irradiation on the current-biased Pb-Pb Josephson junctions is investigated. We report on the observation of hysteretic Shapiro-like steps, indicating that features of coherent transport can be preserved even in competition with significant phase diffusion.