Signatures of Majorana bound states in transport properties of hybrid structures based on helical liquids

Majorana bound states can emerge as zero-energy modes at the edge of a two-dimensional topological insulator in proximity to an ordinary s-wave superconductor. The presence of an additional ferromagnetic domain close to the superconductor can lead to their localization. We consider both normal-metal–superconductor (N-S) and Josephson (S-N-S) junctions based on helical liquids and study their spectral properties for arbitrary ferromagnetic scatterers in the normal region. Thereby, we explicitly compute Andreev wave functions at zero energy. We show under which conditions these states form localized Majorana bound states in N-S and S-N-S junctions. Interestingly, we can identify Majorana-specific signatures in the transport properties of N-S junctions and the Andreev bound levels of S-N-S junctions that are robust against external perturbations. We illustrate these findings with the example of a ferromagnetic double barrier (i.e., a quantum dot) close to the N-S boundaries.