Description:
Semiconductor–superconductor hybrid systems are promisingcandidates for the realization of Majorana fermions and topological order, i.e.topologically protected degeneracies, in solid state devices. We show that thetopological order is mirrored in the excitation spectra and can be observedin nonlinear Coulomb blockade transport through a ring-shaped nanowire.Especially, the excitation spectrum is almost independent of magnetic flux inthe topologically trivial phase but acquires a characteristic h/e magnetic fluxperiodicity in the non-trivial phase. The transition between the trivial and nontrivialphase is reflected in the closing and reopening of an excitation gap. Weshow that the signatures of topological order are robust against details of thegeometry, electrostatic disorder and the existence of additional subbands andonly rely on the topology of the nanowire and the existence of a superconductinggap. Finally, we show that the coherence length in the non-trivial phase is muchlonger than in the trivial phase. This opens the possibility to coat the nanowirewith superconducting nanograins and thereby significantly reduce the currentdue to cotunnelling of Cooper pairs and to enhance the Coulomb charging energywithout destroying the superconducting gap.