Systems with a flat Chern band have been extensively studied for their potential to realize high-temperature fractional quantum Hall states. To experimentally observe the quantum transport properties, a sizable topological gap is highly necessary. Here, taking advantage of the high tunability of two-dimensional (2D) metal-organic frameworks (MOFs), whose crystal structures can be easily tuned using different metal atoms and molecular ligands, we propose a design of a 2D MOF [Tl2(C6H4)3, Tl2Ph3] showing nontrivial topological states with an extremely large gap in both the nearly flat Chern band and the Dirac bands. By coordinating π-conjugated thallium ions and benzene rings, crystalline Tl2Ph3 can be formed with Tl and Ph constructing honeycomb and kagome lattices, respectively. The px,y orbitals of Tl on the honeycomb lattice form ideal pxy four-bands, through which a flat Chern band with a spin-orbit coupling (SOC) gap around 140 meV evolves below the Fermi level. This is the largest SOC gap among all the theoretically proposed organic topological insulators so far.
Bibliographical noteFunding Information:
N. Su and F. Liu are supported by U.S. DOE-BES (Grant No. DE-FG02-04ER46148). W. Jiang is supported by the National Science Foundation-Material Research Science & Engineering Center (NSF-MRSEC Grant No. DMR-1121252). We also thank the CHPC at the University of Utah and DOE-NERSC for providing the computing resources.
© 2018 Author(s).