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Observation of surface ferromagnons in the axion-insulating phase of the antiferromagnetic topological insulator EuSn2As2

Mamoun Hemmida1,*, Santanu Pakhira2,3, David C. Johnston2,4, and Hans-Albrecht Krug von Nidda1,†

  • *Contact author: Mamoun.hemmida@physik.uni-augsburg.de
  • †Contact author: Hans-albrecht.krug@physik.uni-augsburg.de
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Phys. Rev. Research 8, 023309 – Published 17 June, 2026

DOI: https://doi.org/10.1103/dp4g-dyll

Abstract

We report the study of spin dynamics of Eu2+ in the antiferromagnetic axion topological insulator EuSn2As2 by means of antiferromagnetic resonance at 9.34 GHz. Below the Néel temperature (TN), two types of resonance modes, the conventional bulk antiferromagnetic resonance and additional surface ferromagnetic resonance, are observed. The latter turns out to be characteristic of the axion-insulating phase. Above TN, we prove the existence of a Kosterlitz-Thouless scenario that is relevant for the spin relaxation in the Eu2+ layers. The absence of Korringa relaxation indicates the strong confinement of the conduction electrons at the Fermi level to the SnAs layers.

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Phys. Rev. Research 8, 023309– Published 17 June, 2026
  • Received 26 September 2023
  • Revised 23 February 2024
  • Accepted 9 May 2026
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