CPM Seminar

Proposed Realization and Signatures of Floquet Topological Superconductors and Insulators

Babak Seradjeh

Indiana University

As understood recently, a topologically nontrivial electronic state may be generated dynamically in an otherwise normal combination of materials by a periodic driving force. Such a state can only occur when the system is driven out of equilibrium. A Floquet topological insulator can be realized, for example, in a two-dimensional system of Dirac fermions, such as graphene, irradiated by a circularly polarized laser. It is characterized by steady state edge modes and two separate integer-valued topological invariants. A Floquet topological superconductor, on the other hand, is characterized by two types of Floquet Majorana fermions� - steady states of equal superposition of electrons and holes� - with a period that is the same or twice that of the drive. I introduce these concepts and present our recent theoretical work on the realization and detection of Floquet topological states. Floquet Majorana fermions can be realized in a highly tunable setup consisting of two coupled quantum dots and detected by a third probe dot. More generally, Floquet Majorana fermions can be detected by measuring a quantized conductance sum rule over discrete values of lead bias differing by multiples of drive frequency. This quantized sum rule is robust against weak disorder. Finally, I present an effective theory of Floquet topological insulator in irradiated graphene and use it to study its transport signature. Remarkably, we find that disorder can enhance transport at certain Floquet topological transitions by several orders of magnitude.