Recent discoveries of intrinsic magnetic topological insulators have generated immense interest since they can generate various topological quantum states, such as quantum anomalous Hall insulators, axion insulators, and Weyl semimetal. In this talk, I will present our recent studies on intrinsic magnetic topological insulators MnBi2nTe3n+1 [1-4]. I will first report on our discoveries of the field-induced ideal Weyl state in MnBi2Te4 [2]. Through fine chemical potential tuning by Sb substitution for Bi, we have observed transport evidence of a long-sought topological state – an ideal type-II ferromagnetic (FM) Weyl state with one pair of Weyl nodes in the lightly hole-doped samples. Their transport signatures of the Weyl state are manifested by a field-driven electronic structure transition, a negative longitudinal magnetoresistance attributable to the chiral anomaly, as well as a large intrinsic anomalous Hall effect in the FM phase. Furthermore, we also revealed a giant spin-valve effect in the lightly electron-doped samples, sharply contrasted with the chiral anomaly behavior observed in the lightly hole-doped samples, which indicates Weyl fermions are not susceptible to magnetic scattering [3]. Finally, I will also discuss the possibility of the Weyl state driven by spontaneous ferromagnetism in heterostructural compounds Mn(Bi1-xSbx)2nTe3n+1 with n = 2 & 3.

1Lee et al., Physical Review Research 1, 012011 (2019)

2Lee et al., Physical Review X 11, 031032 (2021)

3Lee et al., In Review (2022)

4Guan et al, Physical Review Materials 6, 054203 (2022)

The study at PSU 2DCC-MIP is supported by NSF Cooperative Agreement No. DMR-1539916 and DMR-2039351.