Regensburg 2019 – wissenschaftliches Programm
MA 45.8: Vortrag
Donnerstag, 4. April 2019, 12:30–12:45, H15
Fractional charge tunneling between Shiba states in STM devices — •Ciprian Padurariu1, Haonan Huang2, Björn Kubala1, Simon Dambach1, Christian R. Ast2, and Joachim Ankerhold1 — 1Institute for Complex Quantum Systems and IQST, Ulm University, 89069 Ulm, Germany — 2Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany
We present the theory and experimental realization of tunneling between tip and substrate Shiba states in superconducting STM devices operating at 15 mK. The simple analytical results are in good agreement with conductance measurements exhibiting peaks in the tunnel current at a number of sub-gap bias voltages.  The voltages are identified as resonances of sub-gap discrete magnetic states, so called Shiba states, that form inside a volume around the magnetic impurity of coherence length size. 
When a Shiba state formed around an impurity in the STM tip is brought into proximity with a Shiba state formed around an impurity in the substrate, new resonances arise at characteristic values of the voltage. The tunnel current at the new resonances is a result of the interplay between coherent transport processes and incoherent relaxation. The elementary transport process carries a fractional charge proportional to the electron-hole asymmetry in the device.
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