Evolution of the Electronic Structure of Ultrathin MnBi₂Te₄ Films

Abstract

Ultrathin films of intrinsic magnetic topological insulator MnBi2Te4 exhibit fascinating quantum properties such as the quantum anomalous Hall effect and the axion insulator state. In this work, we systematically investigate the evolution of the electronic structure of MnBi2Te4 thin films. With increasing film thickness, the electronic structure changes from an insulator type with a large energy gap to one with in-gap topological surface states, which is, however, still in drastic contrast to the bulk material. By surface doping of alkali-metal atoms, a Rashba split band gradually emerges and hybridizes with topological surface states, which not only reconciles the puzzling difference between the electronic structures of the bulk and thin-film MnBi2Te4 but also provides an interesting platform to establish Rashba ferromagnet that is attractive for (quantum) anomalous Hall effect. Our results provide important insights into the understanding and engineering of the intriguing quantum properties of MnBi2Te4 thin films.

Emerging Nontrivial Topology in Ultrathin Films of Rare-Earth Pnictides

“…Note, however, that some of the Bi-based compounds already show nontrivial topology in the 3D bulk due to the crossing of the Bi 6 p and the rare-earth 5 d bands near the X point. , The As- and Sb-based compounds are all topologically trivial semimetals and hence are all expected to become topologically nontrivial when made as few monolayers thick, (001)-oriented ultrathin films. Apart from the case of Sc-, Y-, La-, and Lu-based compounds, where the RE 4 f orbitals are completely empty or filled, other RE-Vs exhibit magnetic ordering at low temperatures. − This creates an opportunity to combine nontrivial topology with spin magnetism, potentially leading to the emergence of novel phenomena such as 2D antiferromagnetic topological insulators, − the quantum anomalous Hall effect in Chern insulators, , and the presence of Fermi arcs resulting from an unconventional magnetic splitting . Further discussion on the effect of partially filled 4 f states is provided in Supporting Information, Note S2.…”

Engineering topological states in a two-dimensional honeycomb lattice

“…Generally, the symmetry of the BZ center (G point) is higher than that of the corners (K/K 0 point), thus the Dirac dispersion is more easily broken. 70 Recent experimental results have shown that K can be successfully doped in layered MnBi 2 Te 4 , 71,72 suggesting that K can also be doped in 2D magnetic materials of CrBr 3 , CrCl 3 , and VBr 3 monolayers. Here, we take K-doped CrBr 3 as an example to illustrate their magnetic, electronic, and topological properties.…”

Surface Electronic Structure Engineering of Manganese Bismuth Tellurides Guided by Micro‐Focused Angle‐Resolved Photoemission

“…Intrinsic magnetic topological insulators based on manganesebismuth tellurides (MBTs) have come to prominence DOI: 10.1002/adma.202301907 as extremely attractive designer quantum materials with potential applications in spintronics and topotronics. [1][2][3] Their magnetic, electronic, optical, and topological properties can be widely tuned by various mechanisms of doping, [4][5][6][7] layered synthesis, [2,[8][9][10] and optical excitation. [11][12][13][14] The parent compound in this family of materials is MnBi 2 Te 4 , which consists of ferromagnetic Te-Bi-Te-Mn-Te-Bi-Te septuple layers.…”

“…This picture has proven much too simple in a recent study of alkali-driven electronic structure modifications of MnBi 2 Te 4 bulk and thin films, where surprising hole doping effects were observed. [7,10] The impact of alkali adsorption on the various possible surface terminations of MBT heterostructure compounds has not been investigated and a universal picture of the effect of alkali doping on the MBT family of materials is lacking. Such doping-dependent ARPES studies are complicated by the fact that surface adsorption strongly affects the surface potential of the materials, which in turn impacts the ARPES photoemission intensity through photon energy-dependent matrix element effects.…”