Quantum Floquet anomalous Hall states and quantized ratchet effect in   one-dimensional dimer chain driven by two ac electric fields
  In condensed matter physics, one of the major topics is to find out and classify interesting novel topological matters and phenomena. Topologically nontrivial systems can also be achieved by using periodical driving fields. On the other hand, ratchet effect can be used to collect useful work from fluctuations or realize directed transport in periodically-driven systems. Here, we promote a dimer chain by applying two mutually-perpendicular ac electric fields, and obtain an effective two-dimensional Hamiltonian in the low-frequency regime. We thereby derive quantum Floquet anomalous Hall (QFAH) conductance and then find a quantized ratchet effect in the resulting current along the chain. Our further analysis shows that these originate from the electric fields only. This lengthwise quantized ratchet effect without magnetic field should be useful to designing novel high-performance electronic applications. 
Jin-Yu Zou, Bang-Gui Liu
cond-mat.mes-hall