Site-Selective Electronic Structure and Dynamical Softness in the Metallic Antiferromagnet Mn3CuN

Electronic structure, local bonding, and magnetic order are intimately coupled in correlated antiperovskites, making it challenging to distinguish the contributions of individual crystallographic sites to their collective properties. Here, we combine element-specific X-ray spectroscopy, temperature-dependent X-ray absorption spectroscopy, X-ray magnetic circular dichroism, electrical transport measurements, and first-principles calculations to investigate the site-selective electronic structure of epitaxial metallic antiferromagnetic Mn3CuN thin films. We reveal an anomalous charge distribution characterized by effective low-valent Mn and subvalent Cu states stabilized by covalent Mn-N-Cu interactions. While the Mn sublattice forms a robust noncollinear antiferromagnetic framework below ∼120 K, the electronically distinct Cu sites remain magnetically inactive yet exhibit pronounced temperature-dependent local structural evolution. Despite the onset of magnetic ordering, Mn3CuN retains metallic transport with a near-zero temperature coefficient of resistivity (NZ-TCR), indicating minimal coupling between magnetic ordering and charge transport. These findings demonstrate that site-selective electronic structure enables chemically differentiated lattice dynamics while preserving a robust magnetic framework, establishing Mn3CuN antiperovskite in which electronic, structural, and magnetic responses can be selectively decoupled. This work provides a materials design principle for engineering multifunctional metallic antiperovskites through site-selective electronic structure and local chemical bonding.