Transition from Majorana to Weyl fermions and anapole moments

Abstract

The apparent splitting of zero-bias conductance peaks, observed in recent experiments concerning Majorana fermions in nanowires coupled to superconductors, can be interpreted as a manifestation of a transition in the structure from (massive) Majorana to (massless) Weyl fermions. A modification of the experiments in order to test such phenomenon is proposed by making recourse to the only possible electromagnetic interaction allowed to (massive) Majorana particles and mediated by their anapole moment. In suitably designed heterostructures with toroidal symmetry, the additional anapole interaction manifests itself in the lowering of the critical magnetic field required for the appearance of the zero-bias peak, a shift that can be directly measured and thus reveal the presence of Majorana (rather than Weyl) fermions. Anapole interactions, though not previously considered, may also be a powerful method to control the dynamics of Majorana fermions, and then to manipulate the qubit state in quantum computation.