Quasicrystalline Altermagnetism

Abstract: Altermagnets are a recently discovered class of magnetic materials that combine a collinear, zero-magnetization spin structure, characteristic of antiferromagnets, with spin-split electronic bands, a hallmark of ferromagnets. This unique behavior arises from the breaking of combined time-reversal and spatial symmetries (such as inversion or lattice translation), which are preserved in conventional antiferromagnets. To date, research has focused on altermagnetic phases in periodic crystals, where the order is linked to specific crystallographic rotation symmetries. In this work, we demonstrate that quasicrystals, which possess rotational symmetries forbidden in periodic lattices, can host exotic altermagnetic orders. Using symmetry analysis and self-consistent mean-field theory, we predict stable $g$-wave and $i$-wave altermagnetism in octagonal and dodecagonal quasicrystals, respectively. These novel phases are characterized by global $C_8T$ and $C_{12}T$ symmetries and manifest as unique anisotropic spin-splittings in their spectral functions and spin conductance, featuring characteristic eight- and twelve-fold nodal structures that serve as unambiguous experimental fingerprints. Our findings establish quasicrystals as a versatile platform for realizing unconventional altermagnetic orders beyond the constraints of crystallographic symmetry.