Spontaneous anomalous Hall effect arising from an unconventional compensated magnetic phase in a semiconductor

TL;DR

This study reports a spontaneous anomalous Hall effect in a semiconductor MnTe, caused by an unconventional magnetic phase with strong time-reversal symmetry breaking despite zero net magnetization.

Contribution

It reveals a new mechanism for the anomalous Hall effect arising from an unconventional magnetic phase in a semiconductor without net magnetization.

Findings

Spontaneous anomalous Hall signal observed in MnTe without external magnetic field.

The effect is due to an unconventional phase with broken time-reversal symmetry.

Anisotropic crystal environment is crucial for the effect.

Abstract

The anomalous Hall effect, commonly observed in metallic magnets, has been established to originate from the time-reversal symmetry breaking by an internal macroscopic magnetization in ferromagnets or by a non-collinear magnetic order. Here we observe a spontaneous anomalous Hall signal in the absence of an external magnetic field in an epitaxial film of MnTe, which is a semiconductor with a collinear antiparallel magnetic ordering of Mn moments and a vanishing net magnetization. The anomalous Hall effect arises from an unconventional phase with strong time-reversal symmetry breaking and alternating spin polarization in real-space crystal structure and momentum-space electronic structure. The anisotropic crystal environment of magnetic Mn atoms due to the non-magnetic Te atoms is essential for establishing the unconventional phase and generating the anomalous Hall effect.