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

Abstract

Fu and Kane have discovered that a topological insulator with induced s-wave superconductivity (gap ∆0, Fermi velocity vF, Fermi energy µ) 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 ∆ 2 0 /µvF. 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.