Nearly Flat Edges and Corner‐Contrasted Spin Polarization in Pentagon‐Structured Altermagnetic 2D MnC 2

Abstract Penta‐structured altermagnets combining boundary‐localized states and symmetry‐driven spin effects have recently emerged as promising candidates for topo‐spintronic materials. In this work, penta‐MnC 2 is explored, a 2D material that hosts a unique set of coexisting quantum features: a fully compensated altermagnetic ground state, nontrivial real topology, spin‐polarized corner states, and nearly flat edge bands. Using first‐principles calculations, it is demonstrated that the corner states exhibit direction‐dependent spin polarization, with spin‐up and spin‐down modes localized at orthogonal corners. Meanwhile, weakly dispersive edge states appear along specific high‐symmetry directions. The combination of these 0D and 1D spin‐polarized boundary modes, together with bulk altermagnetism and real topology, highlights penta‐MnC₂ as a rare and versatile platform for studying the interplay of magnetism, topology, and boundaries in 2D systems.