Emergent Anomalous Hall Effect from Surface States in the Altermagnet MnTe Thin Films

TL;DR

This study clarifies the origins of anomalous Hall effects in MnTe thin films by distinguishing surface and bulk contributions, highlighting the role of surface states and interface chemistry in AHE behavior.

Contribution

The paper introduces a microscopic framework combining first-principles calculations and symmetry models to explain and control AHE in altermagnetic MnTe thin films.

Findings

Surface states dominate AHE at relevant energies.

Surface AHE sign can be reversed by interface chemistry.

Bulk and surface contributions are linked to orbital magnetization.

Abstract

Transport measurements on thin films of the prototypical altermagnet MnTe have reported conflicting phenomena of anomalous Hall effects (AHE), including opposite signs and thickness-independent resistivity. Here we resolve these discrepancies by separating bulk and surface contributions to the AHE for different crystal terminations. Using first-principles calculations and symmetry-based effective models, we show that although the bulk hosts a characteristic $g$-wave Fermi surface, surface states within the bulk gap acquire a ferromagnet-like spin polarization and dominate the AHE at experimentally relevant Fermi energies. While the surface magnetization follows the surface spin sublattice, the resulting AHE is uniquely determined by the bulk N\'eel order for a given termination. Both bulk and surface contributions are closely linked to a small but finite out-of-plane orbital magnetization. Incorporating realistic interfacial chemistry further reveals that a Te capping layer can reverse the surface AHE sign relative to that on an InP substrate. Our results establish a microscopic framework for interpreting and engineering AHE responses in altermagnetic thin films through interface design.