This paper presents the observation of a resonantly enhanced magneto-optical response of massive Dirac fermions in the kagome-lattice magnet TbMn6Sn6. Infrared magneto-optical spectroscopy reveals that interband transitions on massive Dirac bands significantly contribute to the observed resonance in the optical Hall conductivity. An analytical model accurately reproduces the spectral characteristics, demonstrating a robust anomalous Hall response, nearly 20% of the quantized Hall conductance per kagome layer, even at room temperature. These findings establish the general optical response of massive Dirac fermions and its close relation to universal electrodynamics in the quantum anomalous Hall state.

Y. Okamura, K. Shoriki, Y. Nomura, Y. Fujishiro, A. Kitaori, N. Kanazawa, R. Arita, Y. Tokura, Y. Takahashi