Fragile topological band in the checkerboard antiferromagnetic monolayer FeSe

Aiyun Luo,Gang Xu,Zhida Song

doi:10.1038/s41524-022-00707-9

Aiyun Luo, Gang Xu + Show 1 more

Open Access

https://doi.org/10.1038/s41524-022-00707-9

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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 nearly flat band with fragile topology just below the Fermi level. The Wilson loop calculations identify that such fragile topology is protected by the S4z symmetry, which gives rise to a 2D second-order topological insulator that supports the bound state with fractional charge e/2 at the sample corner. This work provides a 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.

Highlights

Topological matters have attracted extensive interest for their distinct and robust bulk-boundary correspondence[1,2,3,4,5]
We mainly focus on the band structures and topological properties in the checkerboard antiferromagnetic (cb-AFM) phase of monolayer
We carry out the calculations without spin-orbit coupling (SOC) of the cb-AFM monolayer FeSe, and plot the corresponding projected density of states (DOS) of the 3d-orbitals on Fe2 ion

Summary

INTRODUCTION

Topological matters have attracted extensive interest for their distinct and robust bulk-boundary correspondence[1,2,3,4,5]. Different from the stable topology, the fragile topology generally cannot exhibit robust edge states. We demonstrate that their low-energy physics can be well captured by a double-degenerate nearly flat band with fragile topology just below the Fermi level, which gives rise to a 2D second-order topological insulator (SOTI) that supports the bound state with fractional charge e/2 at the sample corner. Further analyses find that cb-AFM monolayer FeSe is very close to a well-defined AFM TI with nontrivial spin-Chern number characterized by the Sz symmetry These results can well explain the previous observations of topological edge states and bound state near the Fermi level[46,47], and provide a platform to study the intriguing properties of the magnetic fragile topology

RESULTS

DISCUSSION

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