Majorana and Andreev bound states at the helical edge

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Mr. Felix Keidel (Würzburg University, Germany).

Hybrid structures on the basis of helical edge states in proximity to an s-wave superconductor (S) and ferromagnetic insulators (F) are known to give rise to topological superconductivity and allow for Majorana bound states in regions where both the ferromagnetic and the superconducting gap close. In this talk I will discuss junctions with multiple S and F barriers. The cavities between them can be understood as quantum dots hosting overlapping Majorana (MBS) and Andreev quasi-bound states (ABS). I will show how the resulting hybridization and splitting depend on distinct parameters of the systems. Remarkably, there is a close connection between the localized bound states and the induced nonlocal pairing amplitudes. The anomalous correlations provide a way to distinguish MBS and ABS and exhibit exotic odd-frequency dominated triplet pairing for resonances associated with hybridized MBS. In the last part of the talk I will discuss how one could possibly use the high tunability of these systems in order to facilitate heat currents and the thermoelectric effect.