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MnBi₂Te₄, an intrinsic magnetic topological insulator, has recently been predicted to possess a variety of topological quantum states, including quantum anomalous Hall insulator (QAHI), axion insulator in its 2D thin layers, and an ideal Weyl semimetal state in its bulk ferromagnetic (FM) phase^1-3. QAHI and axion insulator in MnBi₂Te₄ thin layers have been experimentally demonstrated^4,5, but the predicted FM Weyl state remains elusive. In this talk, we report the experimental evidence of the field-induced Weyl state in Mn(Bi_1-xSb_x)₂Te₄⁶. The characteristics of the expected Weyl state were observed when the system is tuned to be lightly hole-doped via Sb substitution for Bi and is manifested by a field-driven electronic phase transition as well as large intrinsic anomalous Hall effect in the FM phase. Our results establish a promising platform for exploring the physics underlying the long-sought, ideal TRS breaking type-II WSM.

¹M. M. Otrokov et al., Nature 576, 416 (2019)
²D. Zhang et al., Phys. Rev. Lett. 122, 206401 (2019)
³J. Li et al., Sci. Adv. 5, eaaw5685 (2019)
⁴Y. Deng. et al., Science 367, 895 (2020)
⁵C. Liu et al., Nat. Mater. 19, 522 (2020)
⁶S. H. Lee et al., arXiv:2002.10683