Altermagnetism in 6H perovskites

The combination of a centrosymmetric crystallographic structure with local structural alternations and collinear antiferromagnetism can lead to broken PT (Parity $\times$ Time-reversal) symmetry, resulting in altermagnets with non-relativistic spin-split bands. The 6H perovskites with composition A$_3$BB'$_2$O$_9$ 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.