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. It is highly desirable to realize directed transport in the absence of magnetic field or magnetization for high-performance applications. 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 conductance and then find a quantized ratchet effect in the resulting current along the chain. This directed electric current, when averaged over one period, is quantized in units of the Hall conductance times the frequency of the main ac field. Our further analysis shows that these originate from the electric fields only. This lengthwise quantized ratchet effect without magnetic field or magnetization should be useful to designing novel robust low-energy-consumption electronic applications.