Zero-energy Andreev bound states from quantum dots in proximitized Rashba nanowires

We study an analytical model of a Rashba nanowire that is partially covered by and coupled to a thin superconducting layer, where the uncovered region of the nanowire forms a quantum dot. We find that, even if there is no topological phase possible, there is a trivial Andreev bound state that becomes pinned exponentially close to zero energy as a function of magnetic field strength when the length of the dot is tuned with respect to its spin-orbit length such that a resonance condition of Fabry-Perot type is satisfied. In this case, we find that the Andreev bound state remains pinned near zero energy for Zeeman energies that exceed the characteristic spacing between Andreev levels but that are smaller than the spin-orbit energy of the dot. Importantly, as the pinning of the Andreev bound state depends only on properties of the dot, we conclude that this behavior is unrelated to topological superconductivity. To support our analytical model, we also perform a numerical simulation of a hybrid system that explicitly incorporates a thin superconducting layer, showing that all qualitative features of our analytical model are present in the numerical results.

References:
Reeg et al, arXiv:1810:09840
Reeg et al, Phys. Rev. B 96, 125426 (2017)
Reeg et al, Phys. Rev. B 97, 165425 (2018)