Altermagnetism in 6H perovskites

The combination of a centrosymmetric crystallographic structure with local structural alternations and collinear antiferromagnetism can lead to broken PT (Parity × Time-reversal) symmetry, resulting in altermagnets with non-relativistic spin-split bands. The 6H perovskites with composition A3BB’2O9 exhibit unique layered structural alternations and typically adopt an antiferromagnetic ground state. Here, we report the discovery that several 6H perovskites are indeed altermagnets exhibiting non-relativistic spin-split bands. We also explore the possible presence of net magnetization due to spin-orbit coupling in these materials, as well as the manifestation of giant piezomagnetism. Since the single crystals of 6H perovskites can be readily grown and cleavable, our findings provide a new avenue to study the cleaved atomically-flat surfaces of altermagnets with advanced experimental techniques such as spin-resolved scanning tunneling microscopy (STM) or spin-resolved angle-resolved photoemission spectroscopy (ARPES) to explore their spin splitting nature.