Colossal Magnetic-Field-Induced Anomalous Hall Conductivity in a Kagome Antiferromagnet YMn₆Sn₆

Kagome-lattice magnets provide a fertile ground for exploring exotic electronic phases due to topological band structures and complex magnetic orders. Yet, how these ingredients dictate unconventional magnetotransport responses, crucial for possible spintronic applications, has remained elusive. Here, we show that a prototypical kagome antiferromagnet ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ exhibits significant magnetic-field-driven redistribution of Berry curvature and the colossal anomalous Hall conductivity (AHC). Under high magnetic fields, spin canting induces a pronounced spin splitting of the flat and Dirac bands near the Fermi level, dramatically enhancing the Berry curvature. The resulting AHC reaches $\sim$ 2.5 $\times$ 10 ${}^4$ S/cm, far exceeding the intrinsic Berry curvature predictions and ranking among the highest reported in magnetic systems. This colossal AHC enhancement is attributed to a synergy between field-tuned Berry curvature and enhanced skew scattering in the clean limit. Our findings highlight the critical role of magnetic-field-controlled spin splitting in engineering Berry curvature and anomalous magnetotransport in clean kagome magnets.