Multiple Andreev reflections in s-wave superconductor-quantum dot- topological superconductor tunnel junctions and Majorana bound states

TL;DR

This paper investigates the current-voltage characteristics of a superconductor-quantum dot-topological superconductor junction, highlighting how Majorana bound states produce distinctive, magnetic field-robust signatures in tunneling behavior.

Contribution

It provides a detailed analysis of multiple Andreev reflections in such junctions and identifies magnetic field robustness as a key signature of Majorana bound states.

Findings

MBS cause distinctive I-V features robust to magnetic field changes.

The I-V curve exhibits a two-dot shape with multiple Andreev reflection peaks.

Magnetic field dependence can distinguish MBS from other zero-energy states.

Abstract

We calculate the current as a function of applied voltage in non-topological s-wave superconductor-quantum dot-topological superconductor tunnel junction. We consider the type of TS which hosts two Majorana bound states (MBS) at the ends of a semiconductor quantum wire or of a chain of magnetic atoms in the proximity with s-wave superconductor. We find that the $I-V$ characteristic of such system in the regime of big voltages has a typical two dot shape and is ornamented by peaks of multiple Andreev reflections. We also consider the other options when the zero energy states are created by disorder (here by Shiba states) or by Andreev zero energy bound states at the surface of quantum dot and superconductor. The later are obtained by tuning the magnetic field to a specific value. Unlike the last two cases the MBS $I-V$ curves are robust to change the magnetic field. Therefore, the magnetic field dependence of the tunneling current can serve as a unique signature for the presence of a MBS.