Tunneling dynamics between superconducting bound states at the atomic limit

Abstract

Despite plenty of room at the bo om, there is a limit to the miniaturization of every process. For charge transport this is realized by the coupling of single discrete energy levels at the atomic scale. Here, we demonstrate sequential tunneling between parity protected Yu-Shiba-Rusinov (YSR) states bound to magnetic impurities located on the superconducting tip and sample of a scanning tunneling microscope at 10 mK. We reduce the relaxation of the excited YSR state to the bare minimum and nd an enhanced lifetime for single quasiparticle levels. Our work o ers a way to characterize and to manipulate coupled superconducting bound states, such as Andreev levels, YSR states, or Majorana bound states.

Interplay between Yu-Shiba-Rusinov states and multiple Andreev reflections

“…However, this is very challenging and it continues to be an important open problem [35]. Finally, our theory is ideally suited to describe the tunneling between magnetic impurities exhibiting their respective YSR states, which has been experimentally reported for the first time very recently [24]. This is a problem that we shall tackle in a forthcoming paper.…”

“…To conclude this discussion let us say that the 4 × 4 formalism presented here is not strictly necessary in the case of a single impurity with spin-preserving tunneling, and the transport properties of our model system can be equivalently described within a 2 × 2 formalism (using only the Nambu space). However, the 4 × 4 approach provides a convenient platform that illustrates the key role of the spin and it becomes absolutely necessary in more complex situations like, for instance, those involving the tunneling between magnetic impurities with noncollinear spins [24].…”