Emergence of Diverse Topological States in Ge Doped MnBi2Te4

TL;DR

This study explores how Ge doping in MnBi2Te4 induces a variety of topological states, including Dirac and Weyl semimetals, by tuning the band structure and magnetic phases, revealing potential for novel electronic applications.

Contribution

It systematically maps the topological phase diagram of Ge-doped MnBi2Te4, discovering multiple topological phases and mechanisms for their control, which was not previously understood.

Findings

Identification of two classes of magnetic Dirac semimetals.

Discovery of Weyl semimetal phases at ferromagnetic states.

Ability to tune trivial states into Weyl phases with strain.

Abstract

As an ideal platform for studying interplays between symmetry, topology and magnetism, the magnetic topological insulator (MTI) MnBi2Te4 has attracted extensive attentions. However, its strong n-type intrinsic defects hinder the realizations of exotic phenomena. Stimulated by recent discoveries that Ge doping can efficiently tune the position of Fermi level, here we systematically investigate the band evolution and topological phase diagram with doping concentration from MTI MnBi2Te4 to strong topological insulator GeBi2Te4. Different from magnetically doped Bi2Se3, the topology here is determined by competition of two band inversions arising from band folding of two time-reversal invariant momenta between antiferromagnetic and nonmagnetic/ferromagnetic unit cells. By employing a band momentum mapping method, besides the known MTI phase, remarkably, we find two classes of magnetic Dirac semimetal phases at antiferromagnetic state, two classes of Weyl semimetal phases at ferromagnetic state, and an intermediate trivial state at different doping regions. Interestingly, the trivial state can be tuned into a Weyl phase with two coexisting band inversions and extraordinarily long Fermi arcs by a small strain. Our work reveals diverse topological states with intrinsic quantum phenomena can be achieved with great potential for designing future electronic devices.