Control of the Electronic and Atomic Structure of the Altermagnetic α-MnTe Surface via Substrate-Induced Surfactants

Altermagnets are a novel class of materials with unique momentum dependent spin-polarization of the electronic band structure, which opens up new avenues for spintronic devices. Altermagnetic α-MnTe is particularly interesting for such applications due to its giant spin splitting and the persistence of altermagnetic order up to room temperature. Growth of thin films is, however, challenging and governed by interactions with the substrate. As a result, the surface of α-MnTe thin films exhibits very different atomic structures in dependence of the substrate material. Whereas on SrF2(111) an atomically clean, perfectly (2x2) reconstructed surface forms, on InP(111)A the MnTe surface is always InTe terminated due to super-segregation of In from the substrate to the surface. Most strikingly, the InTe surfactant layer displays a quasi-periodic dislocation network to accommodate the InTe/MnTe lattice mismatch. This leads to the emergence of distinct surface states in dependence of surface termination that strongly affect the electronic band structure at the surface as shown by angle resolved photoemission and tunneling spectroscopy. Thus, control and characterization of the atomic structure of the surface is fundamentally important for understanding the properties of altermagnets and provides room for engineering and tailoring of spin-polarized states in actual devices.