Filling anomaly for general 2D and 3D $C_4$ symmetric lattices

TL;DR

This paper develops symmetry indicator formulas for filling anomalies in 2D and 3D lattices with $C_4$ symmetry, accounting for multiple Wyckoff positions, and applies them to topological insulators and semimetals.

Contribution

It introduces a systematic algorithm using Smith normal form for deriving filling anomaly formulas in complex lattices with multiple atomic positions.

Findings

Correctly describes higher-order hinge states.

Accurately predicts Fermi arcs in 3D semimetals.

Extends symmetry indicators to more complex lattice structures.

Abstract

In this manuscript, we derive symmetry indicator formulas for the filling anomaly on 2D square lattices with and without time reversal, inversion symmetry, or their product, in the presence of spin-orbit coupling. We go beyond previous work by considering lattices with atoms occupying multiple Wyckoff positions. We also provide an algorithm using the Smith normal form that systematizes the derivation. The formulas determine the corner charge in 2D atomic or fragile topological insulators, as well as in 3D insulators and semimetals by studying their 2D slices. We apply our results to a 3D tight-binding model on a body-centered tetragonal lattice, whose projection into the 2D plane has two atoms in the unit cell. Our symmetry indicators correctly describe the higher-order hinge states and Fermi arcs in cases where the existing indicators do not apply.