Gapless Surface Dirac Cone in Antiferromagnetic Topological Insulator MnBi2Te4

Abstract

The recent discovered antiferromagnetic topological insulators in Mn-Bi-Te family with intrinsic magnetic ordering have rapidly drawn broad interest since its cleaved surface state is believed to be gapped, hosting the unprecedented axion states with half-integer quantum Hall effect. Here, however, we show unambiguously by using high-resolution angle-resolved photoemission spectroscopy that a gapless Dirac cone at the (0001) surface of MnBi2Te4 exists between the bulk band gap. Such unexpected surface state remains unchanged across the bulk Né el temperature, and is even robust against severe surface degradation, indicating additional topological protection. Through symmetry analysis and ab-initio calculations we consider different types of surface reconstruction of the magnetic moments as possible origins giving rise to such linear dispersion. Our results reveal that the intrinsic magnetic topological insulator hosts a rich platform to realize various topological phases such

Universal gapless Dirac cone and tunable topological states in (MnBi2Te4)m(

“…This is in sharp contrast to the earlier reports of a magnetic order induced surface gap in the order of hundred-meVs in both MnBi2Te4 [2,4,9,17] and MnBi4Te7 [14,15]. On the contrary, our results are consistent with the recent observation of a gapless TSS in MnBi2Te4 [32][33][34][35]. We note that the gapless TSSs in our experiments persist to high temperatures above the magnetic transition temperatures of the materials (supplementary Fig.…”

“…1a) [9][10][11]. However, unexpected gapless topological surface states (TSSs) are observed by high-resolution ARPES measurements [32][33][34][35], raising critical questions regarding the surface magnetic structure, magnetic coupling strength and the specifics of the MnBi2Te4 material system.…”

“…In MnBi2Te4, several magnetic structures have been suggested to produce the gapless TSSs (Fig. 3m), including A-type antiferromagnetic order with in-plane magnetic moment, G-type antiferromagnetic order (magnetic moments aligned antiferromagnetically both in plane and between adjacent layers) and 6 disordered magnetic moments (or paramagnetic state) [32]. We have performed density functional theory (DFT) calculations and confirmed that the gapless TSSs can also be induced by these magnetic structures in MnBi4Te7 and MnBi6Te10.…”

Dirac Surface States in Intrinsic Magnetic Topological Insulators EuSn2As2 and Li1, Gao2, Duan3 et al. 2019Phys. Rev. X259101142View full textAdd to dashboardCite

“…Note added. We become aware of a similar study [43,44] showing the gapless Dirac SSs in MnBi2Te4 when finalizing the present paper.…”

Flat Chern Band from Twisted Bilayer MnBi2Te4

“…This motivates us to consider the Moiré superlattice of TR breaking layered materials. A promising system is 3D antiferromagnetic (AFM) topological axion insulator MnBi 2 Te 4 [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77], which can be driven into a ferromagnetic (FM) Weyl semimetal or 3D QAH insulator. The material consists of Van der Waals coupled septuple layers (SLs) and is FM within each SL.…”