Pressure-Induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator

Recently, natural van der Waals heterostructures of (MnBi_2Te_4)_m(Bi_2Te_3)_n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. We systematically investigate both the structural and electronic responses of MnBi_2Te_4 and MnBi_4Te_7 to external pressure. In addition to the suppression of antiferromagnetic order, MnBi_2Te_4 is found to undergo a metal–semiconductor–metal transition upon compression. The resistivity of MnBi_4Te_7 changes dramatically under high pressure and a non-monotonic evolution of \rho (T) is observed. The nontrivial topology is proved to persist before the structural phase transition observed in the high-pressure regime. We find that the bulk and surface states respond differently to pressure, which is consistent with the non-monotonic change of the resistivity. Interestingly, a pressure-induced amorphous state is observed in MnBi_2Te_4, while two high-pressure phase transitions are revealed in MnBi_4Te_7. Our combined theoretical and experimental research establishes MnBi_2Te_4 and MnBi_4Te_7 as highly tunable magnetic topological insulators, in which phase transitions and new ground states emerge upon compression.