Marc Vila Tusell
Altermagnets, magnetic materials with zero magnetization and spin split band structure, have gained tremendous attention recently for its rich physics and potential applications. However, many theoretical predictions rely on simple effective models that may not represent realistic materials or capture altermagnetism in its full complexity. In this talk, we introduce a tight-binding model that provides a microscopic understanding on how altermagnetism emerges from the interplay between sublattice, orbital and spin degrees of freedom and local crystal field effects [1]. Our design is general, and we apply it to both d-wave and g-wave altermagnets. For d-wave altermagnets, we find that the orbital and spin degrees of freedom are coupled, which gives rise to a momentum-dependent and spin-selective optical absorption. This promotes the controlled optical excitation of up or down spins depending on the polarization direction of linearly polarized light. Such an effect originates from the coupling of orbitals to the sublattice degree of freedom through the crystal field, which is then coupled to spins through the antiferromagnetic interaction. We further propose clear magneto-optical signatures to test our predictions. Regarding g-wave altermagnets, we apply our model to understand the energy splittings and orbital symmetry of the recently measured van der Waals altermagnetic material CoNb4Se8 [2, 3]. Our findings not only demonstrate unique optical manipulation of orbitals and spins in altermagnets but also clarify the fundamental role of crystal field in these novel magnetic materials.
[1] M. Vila, V. Sunko and J.E. Moore, arXiv:2410.23513, 2024[2] R.B. Regmi et. al. arXiv:2408.08835, 2024
[3] N. Dale et. al. arXiv:2411.18761, 2024