Realizing Haldane Model in Fe-based Honeycomb Ferromagnetic Insulators 

Nov. 16 (Wed), 4p.m., #1323(E6-2. 1st fl.)

Dr. Heung-Sik Kim , University of Toronto  

The topological Haldane model (THM) on a honeycomb lattice is a prototype of systems hosting topological phases of matter without external fields. It is the simplest model exhibiting the quantum Hall effect without Landau levels, which motivated theoretical and experimental explorations of topological insulators and superconductors. Despite its simplicity, its realization in condensed matter systems has been elusive due to a seemingly difficult condition of spinless fermions with sublattice-dependent magnetic flux terms. While there have been theoretical proposals including elaborate atomic-scale engineering, identifying candidate THM materials has not been successful, and the first experimental realization was recently made in ultracold atoms. Here we suggest that a series of Fe-based honeycomb ferromagnetic insulators, AFe2(PO4)2 (A=Ba,Cs,K,La) possess Chern bands described by the THM. While BaFe2(PO4)2 fails to exhibit quantized Hall effect due to the filling of even and odd Chern bands, we predict that compounds with A=K,Cs,La have nontrivial bulk Chern numbers with well-defined gap, thereby enabling a solid state realization of THM. 

Contact: MyungJoon Han, Physics Dept., (mj.han@kaist.ac.kr)