Topological Electronic Structure and Intrinsic Magnetization in MnBi4Te7 : A

Abstract

and Anna Isaeva (anna.isaeva@tu-dresden.de) ¥ These authors contributed equally to this work. 2 Combinations of non-trivial band topology and long-range magnetic order hold promise for realizations of novel spintronic phenomena, such as the quantum anomalous Hall effect and the topological magnetoelectric effect. Following theoretical advances material candidates are emerging. Yet, a compound with a band-inverted electronic structure and an intrinsic net magnetization remains unrealized. MnBi2Te4 is a candidate for the first antiferromagnetic topological insulator and the progenitor of a modular (Bi2Te3)n(MnBi2Te4) series. For n = 1, we confirm a non-stoichiometric composition proximate to MnBi4Te7 and establish an antiferromagnetic state below 13 K followed by a state with net magnetization and ferromagnetic-like hysteresis below 5 K. Angleresolved photoemission experiments and density-functional calculations reveal a topological surface state on the MnBi4Te7(0001) surface, analogous to the non-magnetic parent compound Bi2Te3. Our results render MnBi4Te7 as a band-inverted material with an intrinsic net magnetization and a complex magnetic phase diagram providing a versatile platform for the realization of different topological phases.Soon after the discovery of topological insulators (TIs) a decade ago 1 , the role of magnetism and its potential to modify the electronic topology emerged as a central issue in the field of topological materials. Magnetic degrees of freedom provide a powerful means of tuning the decisive characteristic of any topological system: its symmetry. By now it is recognized that the interplay between magnetic order and electronic topology offers a rich playground for the realization of exotic topological states of matter, such as the quantum anomalous Hall state, 2,3 the axion insulator state, 4-6 and magnetic Weyl and nodal lines semimetals, 7-9 enabling in turn different routes to spintronic applications. [10][11][12] The non-trivial topology in paradigmatic TIs like Bi2Te3 is a result of band inversion driven by strong spin-orbit interaction. 13,14 Until recently, the interplay with magnetism in this class of systems has been mostly explored by extrinsic methods, such us doping a known TI

Magnetized topological insulator multilayers

“…The van der Waals character of MBX materials allows for property variation by changing the stacking sequence of magnetic septuple and nonmagnetic quintuple layers (30,35,(37)(38)(39). Importantly, the magnetic field needed to convert between antiferromagnetic and ferromagnetic stacking arrangements can be reduced simply by inserting nonmagnetic quintuple spacers between the magnetic septuple layers.…”

“…We consider the family of bulk crystals in which a template with M MnBi2X4 septuple layers and N Bi2X3 quintuple layers is repeated. Several of these superlattices have already been realized experimentally, including (M,N) = (1,1) (MnBi4Te7) (30,(37)(38)(39), (M,N) = (1,2) (MnBi6Te10) (37,39), and (M,N) = (1,3-6) (MnBi8Te13, MnBi10Te16, and MnBi12Te19) (39). In Fig.…”

“…In agreement with theoretical predictions (9,12), neutron scattering measurements (17,26,30) show that bulk MnBi2X4 (MBX) has A-type antiferromagnetic order with Mn ions ordered ferromagnetically within each septuple layer and antiferromagnetically between adjacent septuple layers. Because the antiferromagnetic interactions between septuple layers are weak, the Mn layer moments in thin films can be aligned by magnetic fields ∼5 T. Thin films can be obtained either by epitaxial growth or by mechanical exfoliation from bulk crystals (8,30,31,(34)(35)(36)(37)(38)(39). Magnetic fields establish quantum Hall effects in thin films not by establishing Landau quantization, but by changing the magnetic configuration from antiferromagnetic to ferromagnetic through overcoming the weak interlayer exchange interactions (21,23,29).…”

Intrinsic magnetic topological insulators

“…also have intrinsic magnetic topological bands. [69][70][71][72][73][74][75][76][77][78][79][80] In these materials, the MBT layers are separated by n layers of Bi 2 Te 3 , as shown in Figure 8C. The interlayer AFM interactions decrease quickly as the distance between MBT layers increases, so the magnetic and topological properties are highly tunable by the number n of Bi 2 Te 3 layers.…”

3D ANALYTICAL MODELING OF CRYSTALLIZATION SURFACES OF THE MnTe–SnTe–Sb2Te3 SYSTEM

“…Tetradymite-type layered ternary phases of the quasi-binary A IV (A VII ) Te-B V 2 Te 3 (A IV = Ge, Sn, Pb; A VII = Mn; B V 2 = Sb, Bi) systems hake been intensively studied as three-dimensional topological insulating materials [1][2][3][4][5]. Among them manganese contained layered phases have especially gained substantial attention since MnBi 2 Te 4 and other ternary manganese-bismuth tellurides possess both topological insulating (TI) and magnetic properties at the same time [6][7][8][9][10][11][12][13][14].…”