Altermagnetism without crystal symmetry
Speaker: Dr Peru d’Ornellas, Institut Néel
Altermagnetism (AM) has gained recognition in the last few years as a new form of collinear magnetism, distinct from ferromagnetism (FM) and antiferromagnetism (AFM). It was defined by expanding our classification to account for symmetries in real space as well as spin space, where altermagnetism emerged as a distinct class which remains invariant under combined time-reversal and real-space rotation. This phase shares features both with FM and AFM; altermagnets have a spin-split band structure but with zero net magnetisation. This formulation—in terms of real space rotations—has guided the search for a physical realisation towards crystalline materials that share the symmetries of the desired phase. Here we show that this is unnecessary. AM can emerge in a completely disordered material from a Hamiltonian that does not explicitly break any spin symmetries and preserves rotation symmetry, albeit on average. Rather, AM emerges due to spontaneous symmetry breaking in the spin and orbital degrees of freedom around each atom. This phase is, analogous to ferromagnetism in disordered media, formed by placing each atom in an identical spin-orbital configuration and so is indifferent to lattice geometry. Spin-resolved conductance and spectral signatures are calculated, verifying that our model exhibits the signature characteristics of an altermagnetic phase.