Transport signatures of a Floquet topological transition at the helical edge

Recently, the experimental realization of a quantum point contact (QPC) between helical edges has been accomplished. We predict that such a QPC, in the presence of a time periodic applied electric field, is characterized by a topological quantum phase transition in the Floquet spectrum. Crucially, the fact that the QPC is naturally attached to helical leads allows for the unambiguous detection of the topological Floquet quantum phase transition by means of multiterminal transport experiments. Moreover, such experiments enable the characterization of the topological bound states associated with the transition.