Competing magnetic orderings and tunable topological states in two-dimensional hexagonal organometallic lattices

The exploration of topological states is of significant fundamental and practical importance in contemporary condensed matter physics, for which the extension to two-dimensional (2D) organometallic systems is particularly attractive. Using first-principles calculations, we show that a 2D hexagonal triphenyl-lead lattice composed of only main group elements is susceptible to a magnetic instability, characterized by a considerably more stable antiferromagnetic (AFM) insulating state rather than the topologically nontrivial quantum spin Hall state proposed recently. Even though thisAFMphase is topologically trivial, it possesses an intricate emergent degree of freedom, defined by the product of spin and valley indices, leading to Berry curvature-induced spin and valley currents under electron or hole doping. Furthermore, such a trivial band insulator can be tuned into a topologically nontrivial matter by the application of an out-of-plane electric field, which destroys the AFM order, favoring instead ferrimagnetic spin ordering and a quantum anomalous Hall state with a nonzero topological invariant. These findings further enrich our understanding of 2D hexagonal organometallic lattices for potential applications in spintronics and valleytronics.National Research Foundation of Korea (NRF) - Korean Government [2015R1A2A2A01003248]; National Natural Science Foundation of China [11174009, 61434002]; National Key Basic Research Program of China [2013CB921900, 2014CB921103]; KISTI supercomputing center [KSC-2014-C3-049]SCI(E)ARTICLEjfeng11@pku.edu.cn; chojh@hanyang.ac.kr49