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Disputation Martina Trahms

Jun 19, 2024 | 10:00 AM
Thema der Dissertation:
Josephson spectroscopy of single atoms in a scanning tunneling microscope
Abstract: Josephson junctions are formed in a scanning tunneling microscope (STM) between a superconducting tip and sample. The influence of the atomic junction composition on the phase coherence between the macroscopic wavefunctions of the electrodes of the Josephson junction is investigated.
In this study, the Josephson junction is exposed to a high frequency (HF) electromagnetic field. Tunneling charge carriers can absorb quantized energy from the photons of the HF field (photon-assisted tunneling). In Josephson contacts coherent absorption of energy from the external field is possible (Shapiro steps). In the presence of the HF field, resonant absorption is observed as steps in the V(I)-characteristics of the junction at the expected energies. A hysteretic behaviour with respect to the direction of the applied current indicates phase coherence between Cooper pair tunneling events while other features of the V(I)- curves are correlated to dissipative processes.
Additionally, Josephson spectroscopy was performed on single magnetic adatoms on the Pb(111) 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 behaviour, i.e. the transition from the resistive single-particle conductance into the Cooper-pair tunneling regime depends on the direction of the applied current. In collaboration with the theory group of Felix von Oppen at Freie Universität Berlin the observed non-reciprocity was correlated to the damping properties of the Josephson junction and explained by the electron-hole asymmetry of the YSR bound states.

Time & Location

Jun 19, 2024 | 10:00 AM

Hörsaal A (1.3.14)
Fachbereich Physik, Arnimallee 14, 14195 Berlin