Achieving quantized transport in Floquet topological insulators via energy filters

Due to photon-assisted transport (PAT) processes, chiral edge modes induced by periodic driving do not directly mediate quantized transport. In the case of particle transport, PAT creates additional transport pathways that break the conductance quantization. In thermal transport, those processes break the energy conservation and lead to heating. Here we show how narrow bandwidth "energy filters'' can restore quantization of both particle and thermal conductance by suppressing PAT through Floquet sidebands. We derive a Floquet Landauer type equation to describe transport through such an energy-filtered setup, and show how the filter can be integrated out to yield a sharply energy-dependent renormalized system-lead coupling. We show analytically and through numerical simulations that a nearly quantized electrical and thermal conductance can be achieved in both off-resonantly and resonantly induced quasienergy gaps when filters are introduced. We introduce a "Floquet distribution function'' and show both analytically and numerically that it approaches the equilibrium Fermi-Dirac form when narrow-band filters are introduced, highlighting the mechanism that restores quantized transport.