# The classification of surface states of topological insulators and superconductors with magnetic point group symmetry

## TL;DR

This paper exhaustively classifies surface states of 3D topological insulators and superconductors with magnetic point group symmetry, using Clifford algebra extension problems and character formulas to identify higher-order topological phases.

## Contribution

It provides a comprehensive classification framework for surface states considering magnetic point group symmetry, extending previous methods with new character formulas.

## Key findings

- Classification of surface states for all magnetic point groups
- Identification of conditions for higher-order topological phases
- Connection between Dirac Hamiltonian mass terms and atomic insulators

## Abstract

We present the exhaustive classification of surface states of topological insulators and superconductors protected by crystallographic magnetic point group symmetry in three spatial dimensions. Recently, Cornfeld and Chapman [Phys. Rev. B {\bf 99}, 075105 (2019)] pointed out that the topological classification of mass terms of the Dirac Hamiltonian with point group symmetry is recast as the extension problem of the Clifford algebra, and we use their results extensively. Comparing two-types of Dirac Hamiltonians with and without the mass-hedgehog potential, we establish the irreducible character formula to read off which Hamiltonian in the whole $K$-group belongs to fourth-order topological phases in three spatial dimensions, which are equivalent to atomic insulators consisting of atoms localized at the point group center.

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Source: https://tomesphere.com/paper/1907.09354