Surface-State-Driven Anomalous Hall Effect in Altermagnetic MnTe Films

TL;DR

This study demonstrates that the anomalous Hall effect in MnTe altermagnetic films is driven by surface states, with experimental and theoretical evidence showing control via interface engineering and a connection to bulk altermagnetic order.

Contribution

It reveals that surface states, rather than bulk bands, dominate the anomalous Hall effect in MnTe films, linking surface transport to bulk altermagnetism through combined experiments and calculations.

Findings

Surface states cross the Fermi level and cause the AH effect.

AH sign reversal occurs near 175 K.

Interface engineering controls the AH response.

Abstract

Altermagnets have recently emerged as a new class of magnetic materials that combine compensated magnetic order with spin-split electronic band structures. In this work, we employ molecular beam epitaxy to grow MnTe thin films with controlled thickness on InP(111)A substrates. By performing angle-resolved photoemission spectroscopy measurements, we observe a large spin splitting of ~230 meV for bulk bands well below the Fermi level and identify surface states that cross the Fermi level. Electrical transport measurements reveal that a robust anomalous Hall (AH) effect persists down to 2 K and an AH sign reversal occurs near 175 K. By systematically tuning film thickness, growth conditions, and interfacial structure, we demonstrate that the AH response in MnTe films originates from the Berry curvature of surface states rather than from bulk bands. Our first-principles calculations reveal that this surface-state-driven AH effect is imprinted by the bulk altermagnetic order and remains unchanged for terminations with opposite Mn magnetic orientations. Our results establish a unique surface transport probe of bulk altermagnetism, demonstrate interface engineering as an effective route to generate and control the AH effect in altermagnets, and provide a unified understanding of the AH response in altermagentic MnTe films.