Nanoscale varying Fermi surface in altermagnetic α-MnTe

Altermagnets exhibit spin-split electronic bands like ferromagnets, yet they are magnetically compensated like collinear antiferromagnets. Altermagnets thus combine the benefits of ferromagnets and antiferromagnets, opening routes to tailored materials and applications. However, reported bulk signatures such as anomalous Hall responses in candidate altermagnets have been inconsistent across samples, suggesting that inhomogeneity may affect their functionality in electronic devices. Here, we use low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to image the nanoscale electronic structure on cleaved surfaces of the altermagnet α-MnTe. As-grown α-MnTe is typically hole-doped due to native defects. However, we resolve two distinct electronic environments: one remains hole-doped with nanoscale variations in its asymmetric gap, while the other exhibits a wider, nearly symmetric gap. Within the hole-doped regions, we discover an incommensurate (~2.5a) charge modulation, highlighting the relevance of nanoscale inhomogeneity for the interpretation of bulk altermagnetic signatures and design of robust altermagnetic devices.