# Surface Magnetism in Topological Crystalline Insulators

## TL;DR

This paper investigates how magnetic impurities induce surface ferromagnetism in topological crystalline insulators, revealing symmetry-dependent magnetic states and analyzing their stability and experimental implications.

## Contribution

It introduces a model showing multiple degenerate magnetic ground states influenced by surface symmetry and electron density, with stability analysis of ferromagnetic phases.

## Key findings

- Surface magnetism depends on surface crystalline symmetry.
- Magnetic states can have twofold, sixfold, or eightfold degeneracy.
- Ferromagnetic states are stable against thermal fluctuations.

## Abstract

We study topological crystalline insulators doped with magnetic impurities, in which ferromagnetism at the surface lowers the electronic energy by spontaneous breaking of a crystalline symmetry. The number of energetically equivalent ground states is sensitive to the crystalline symmetry of the surface, as well as the precise density of electrons at the surface. We show that for a SnTe model in the topological state, magnetic states can have twofold symmetry, sixfold symmetry, or eightfold degenerate minima. We compute spin stiffnesses within the model to demonstrate the stability of ferromagnetic states, and consider their ramifications for thermal disordering. Possible experimental consequences of the surface magnetism are discussed.