Berry-Curvature Activation by Orbital Flux in a Kagome Altermagnet

Abstract

We investigate topological electronic responses in a kagome altermagnetic metal hosting a compensated coplanar $120^\circ$ magnetic texture. Using a minimal tight-binding model incorporating nearest-neighbor hopping, noncollinear exchange coupling, intrinsic spin--orbit coupling, and an emergent orbital chiral flux, we demonstrate that frustrated kagome altermagnets provide a natural platform for realizing momentum-dependent spin splitting and Berry-curvature engineering without net magnetization. The noncollinear exchange field alone generates pronounced altermagnetic spin splitting and spin-polarized Fermi surfaces despite the absence of relativistic effects. However, for a strictly coplanar magnetic state, the system preserves a hidden antiunitary symmetry $\mathcal{T}C_{2z}$, which enforces identically vanishing Berry curvature even in the presence of sizeable spin--orbit coupling. We show that finite Berry curvature emerges only after introducing an orbital chiral flux term that breaks the hidden symmetry and generates effective momentum-space gauge fields analogous to a Haldane-type orbital flux. Remarkably, this mechanism produces local Berry curvature hot spots even in the complete absence of spin--orbit coupling and scalar spin chirality, establishing a purely orbital route toward topological altermagnetism. By systematically analyzing the anomalous Hall conductivity as a function of exchange coupling, spin--orbit interaction, and chiral flux, we identify a hierarchy of competing energy scales governing the transition from a symmetry-protected altermagnetic metal to a topological altermagnetic phase with strong Hall response. Our results demonstrate that frustrated kagome altermagnets constitute a versatile platform for engineering topological transport, Berry curvature, and spin-selective electronic structure in compensated magnetic systems.