Fragile topologically flat band in the checkerboard antiferromagnetic monolayer FeSe

Abstract

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

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Cited by in corpus (10)

• Higher-order topological phases in crystalline and non-crystalline systems: a review
• Sublattice-enriched tunability of bound states in second-order topological insulators and superconductors
• Orbital shift-induced boundary obstructed topological materials with a large energy gap
• Quantum spin Hall effect protected by spin U(1) quasisymmetry
• Spin-Dependent High-Order Topological Insulator and Two Types of Distinct Corner Modes in Monolayer FeSe/GdClO Heterostructure
• Fractional corner charges in threefold-symmetric two-dimensional materials with fragile topology
• Fragile topological phase on the triangular kagome lattice and its bulk-boundary correspondence
• Controllable magnetic anisotropy and ferroelasticity in superconducting FeSe monolayer with surface fluorine adsorption
• Symmetry-breaking-induced topology in FeSe
• Coexistence of d-Wave Altermagnetism and Topological States in Janus FeSeX (X = S, Te) Monolayers