Fragile topological band in the checkerboard antiferromagnetic monolayer FeSe

Abstract By means of the first-principles calculations and magnetic topological quantum chemistry, we demonstrate that low-energy physics in checkerboard antiferromagnetic (AFM) monolayer FeSe, very close to an AFM insulator hosts robust edge states, can be well captured by a double-degenerate nearly flat band with fragile topology just below Fermi level. The Wilson loop identify such is protected S 4 z symmetry, which gives rise 2D second-order supports bound state fractional charge e /2 at sample corner. This work provides platform study intriguing properties electronic states. Previous observations states FeSe also understood our work.