Altermagnetism has emerged as a third type of collinear magnetism. In contrast to standard ferromagnets and antiferromagnets, altermagnets exhibit extra even-parity wave spin order parameters resulting in a spin splitting of electronic bands in momentum space. In real space, sublattices of opposite spin polarization are anisotropic and related by rotational symmetry. In the hitherto identified altermagnetic candidate materials, the anisotropies arise from the local crystallographic symmetry. Here, we show that altermagnetism can also form as an interaction-induced electronic instability in a lattice without the crystallographic sublattice anisotropy. We provide a microscopic example of a two-orbital model showing that the coexistence of staggered antiferromagnetic and orbital order can realize robust altermagnetism. We quantify the spin-splitter conductivity as a key experimental observable and discuss material candidates for the interaction-induced realization of altermagnetism.

<a href= https ror org 04xrcta15 >Munich Center for Quantum Science and Technology < a> Schellingstrasse 4 80799 München Germany

Blackett Laboratory <a href= https ror org 041kmwe10 >Imperial College London< a> London SW7 2AZ United Kingdom

Institut für Physik <a href= https ror org 023b0x485 >Johannes Gutenberg Universität Mainz< a> D 55099 Mainz Germany

Institute of Physics <a href= https ror org 053avzc18 >Czech Academy of Sciences< a> Cukrovarnická 10 162 00 Praha 6 Czech Republic

Technical University of Munich TUM School of Natural Sciences Physics Department TQM 85748 Garching Germany

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Nanoscale imaging and control of altermagnetism in MnTe