Engineering Spin Splitting in Antiferromagnets by Superatoms with Internal Degree of Freedom

Abstract: Superatoms, stable atomic clusters acting as building blocks for new materials, offer unique opportunities due to their rich properties and potential for 2D material assembly. While extensive research has focused on their similarities to ordinary atoms, the role of their internal degrees of freedom (IDOF) remains largely unexplored. Concurrently, compensated antiferromagnets (AFMs) with intrinsic spin-split band structures have emerged as a promising class of materials for spintronics, yet their experimental realization, particularly in two dimensions, is limited. Here, we bridge these two fields by proposing a novel strategy to achieve spin-split AFMs using superatoms with IDOFs. We establish our core concept using a simple model, demonstrating how superatom IDOFs can be leveraged to engineer system symmetry and induce spin splitting in AFM states. We concretely illustrate this strategy by first-principles calculations on a Mo-decorated carborophene sheets, constructed from closo-carborane superatoms. We show that the distinct IDOFs of carborane isomers (electric-dipole-like and nematic) are critical in determining the symmetry of the resulting 2D superatomic crystal and, consequently, the spin splitting pattern of its AFM states. Our findings underscore the profound significance of superatom IDOFs-a feature absent in ordinary atoms-and introduce a new paradigm for engineering spin splitting in AFM lattices. This work opens novel avenues for the design of advanced spintronic and quantum materials based on superatoms.