AC Josephson effect and multiple Andreev reflection currents in nanowire junctions with Majorana fermions

Abstract

Recent experiments have reported conductance measurements in semiconducting nanowire-based systems that support the existence of Majorana bound states (MBS)s at normal-superconductor (NS) junctions. Although these experiments are partially consistent with the Majorana interpretation, other mechanisms such as disorder, Kondo physics, or even Andreev bound states cannot be completely ruled out. It is thus extremely desirable to study further effects that might provide smoking gun signatures for topological superconductivity and Majorana fermions. In this talk, I will discuss how the ac Josephson current in voltage-biased SNS junctions with nanowires in the topological phase contains anomalously long-lived transients that provide unequivocal proof of the existence of MBSs. The multiple Andreev reflection (MAR) currents in such junctions also exhibit unique features related to topology, such as the gap inversion, the formation of MBSs, and fermion-parity conservation. Moreover, the critical current, which remarkably does not vanish at the critical point where the system becomes gapless, provides a direct trace of the topological transition.