Magneto-optical responses of massive Dirac fermions derived from kagome magnet TbMn₆Sn₆

Kagome-lattice magnets have been attracting increasing attention due to the emergence of massive Dirac fermions arising from the unique geometry of atomic lattice, potentially leading to realization of Chern insulator. The massive Dirac fermions are anticipated to show various electromagnetic phenomenon, such as the enhanced intrinsic anomalous Hall effect (AHE) and the quantized AHE, based on the Berry phase theory. The interband transition on massive Dirac bands, which is associated with the quantized AHE, is also expected to exhibit the universal magneto-optical resonance. However, the experimental observation of it is still challenging. In this study, we show magneto-optical responses originating from massive Dirac fermions in the kagome lattice magnet TbMn₆Sn₆. Infrared magneto-optical spectroscopy and first-principles calculations reveal a prominent resonance structure in the optical Hall conductivity. The observed spectra show quantitative agreements with the response function of massive Dirac fermions, establishing their general optical response. DC anomalous Hall conductivity arising from this Hall resonance exceeds 15 % of the quantized value e²/h per one kagome layer even at room temperature.