Controllable and continuous quantum phase transitions in intrinsic magnetic topological insulators

The intrinsic magnetic topological material MnBi₂Te₄ has demonstrated great potential to investigate the interplay between topology and magnetism, which opens up new avenues for manipulating nontrivial electronic states and designing quantum devices. However, challenges and controversies remain due to its inevitable n-type antisite defects, hindering the experimental realization of intrinsic magnetic topological phenomena and rendering the precise control of topological phase transitions (TPTs) unachievable. Here, we study a candidate material family, Mn₍₁−x₎Ge_xBi₂Te₄, in which the heavy n-type doping features are strongly suppressed when the Ge content reaches 0.46, and multiple topological phases are well maintained with the surface Dirac point located near the Fermi level. Based on angle-resolved photoemission spectroscopy, transport measurements, and first-principles calculations, we reveal two magnetism-induced TPTs: the first is an antiferromagnetic-ordering-induced transition from strong topological insulator to a magnetic topological insulator as revealed by gap opening of topological surface states; the second is the external-magnetic-field-dependent transition from magnetic topological insulator to a Weyl semimetal with the gap reclosed. Our work paves the way for the realization of intrinsic magnetic topological states in the MnBi₂Te₄ family and provides an ideal platform for achieving controllable and continuous TPTs toward future spintronic applications.