Chirality inversion of Majorana edge modes in a Fu-Kane heterostructure

TL;DR

This paper demonstrates that the chirality of Majorana edge modes in a Fu-Kane heterostructure can be inverted by supercurrent, leading to doubled thermal conductance and the emergence of a Dirac mode, providing a unique signature of Majorana fermions.

Contribution

It reveals a novel mechanism for inverting Majorana mode chirality via supercurrent, distinct from spinless p-wave systems, and identifies observable signatures of this inversion.

Findings

Chirality of Majorana modes can be inverted by supercurrent.

Inversion doubles the thermal conductance of the edge channel.

Inverted edge supports a nonzero electrical current with a Dirac mode.

Abstract

Fu and Kane have discovered that a topological insulator with induced s-wave superconductivity (gap $\Delta_0$, Fermi velocity $v_{\rm F}$, Fermi energy $\mu$) supports chiral Majorana modes propagating on the surface along the edge with a magnetic insulator. We show that the direction of motion of the Majorana fermions can be inverted by the counterflow of supercurrent, when the Cooper pair momentum along the boundary exceeds $\Delta_0^2/\mu v_{\rm F}$. The chirality inversion is signaled by a doubling of the thermal conductance of a channel parallel to the supercurrent. Moreover, the inverted edge can transport a nonzero electrical current, carried by a Dirac mode that appears when the Majorana mode switches chirality. The chirality inversion is a unique signature of Majorana fermions in a spinful topological superconductor: it does not exist for spinless chiral p-wave pairing.