Evidence of a type-II to type-I Weyl semimetal transition controlled by magnetization rotation

Unlike their high-energy counterpart, the Weyl fermions in the Weyl semimetals (WSMs) do not need to obey the Lorentz symmetry, which allows the Weyl cones to tilt in the energy-momentum space. The tilting of the Weyl cones leads to two kinds of WSMs, type-I and type-II, each hosting distinct Fermi surface topology and magneto-transport properties. In this talk, I will present evidence of a transition from an ideal type-II to type-I WSM phase in MnBi_2-xSb_xTe₄, controlled by an easy knob of magnetic field angle. Evidence includes the anomalous angular dependence of Shubnikov de Haas oscillations and high-field Hall resistivity, both suggesting a Lifshitz transition associated with dramatic changes in Fermi surface topology. Furthermore, an unusual angle dependence of anomalous Hall conductivity further confirms the tilting of the Weyl cones that induces the Lifshitz transition. These findings establish MnBi_2-xSb_xTe₄ as an exceptional platform for exploring Weyl physics and topological phase transitions.