Masters Defense: Mads Kruse – University of Copenhagen

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Masters Defense: Mads Kruse

Energy filtered leads for quantized transport in Floquet systems

Topological insulators are exotic phases of matter that display a variety of interesting physical phenomena. Unlike other insulators these systems are characterized by perfectly conducting states at the edge, that are robust and universal in nature. Recently it was proposed that non-equilibrium phases dubbed Floquet topological insulators could be created using time periodic external fields. Unlike their equilibrium counterpart these new exotic states of matter do not generally display the same physical features. Signatures such as conductance quantization which is present in equilibrium topological phases are absent in Floquet topological insulators due to photon-assisted tunneling. Recently it was proposed that quantization could be restored in these systems by using so called energy filtered leads. In this thesis, we study this strategy from a theoretical viewpoint. Using non-equilibrium Green's functions, numerical results for various physical quantities of these systems are obtained. We find that our method leads to almost perfectly quantized values of differential conductance. In addition several other physical quantities are obtained that further support our results. The method used here can be applied the several other periodically driven topological systems where photon assisted tunneling spoils conductance quantization.