Coexistence of intrinsic magnetic topological state and spin-polarized nontrivial flatband in the honeycomb-kagome monolayers <i>X</i>2Rb3 (<i>X</i>=Cr, Mo, W)

Abstract

Magnetic materials featuring topology and flatband in their electronic structure bridge the topological quantum physics and strongly correlated many-body physics, but materials that manifest this feature are rare. Here, we predict a class of ideal intrinsic magnetic topological insulators naturally featuring a nontrivial flatband in the two-dimensional (2D) honeycomb-kagome lattices X2Rb3 (X=Cr, Mo, W). In the absence of spin–orbit coupling (SOC), these monolayers are spin-polarized half-semimetals with a twofold degenerate nodal point and a flatband appearing at the Fermi level simultaneously. With SOC included, a significant bandgap (168 meV for W2Rb3) opens up at the band touching point, and the flatband that spans the whole Brillouin zone becomes nontrivial with a nonzero Chern number (C = 1). The topological property calculations verify that X2Rb3 monolayers are intrinsic quantum anomalous Hall effect materials. Due to the similarity to 2D continuum Landau levels, the striking nontrivial flatband in X2Rb3 makes it an ideal platform to investigate the flatband physics, such as the realization of fractional quantum anomalous Hall states in real materials.