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 MnBi$_2$Te$_4$ exists between the bulk band gap. Such unexpected surface state remains unchanged across the bulk N\'eel temperature, and is even robust against severe surface degradation, indicating additional topological protection. Through symmetry analysis and $\textit{ab}$-$\textit{initio}$ 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 as topological crystalline insulator and time-reversal-preserved topological insulator, by tuning the magnetic configurations.
Highlights
The integration of magnetic order and topological nontriviality has received much attention since the dawn of the topological era in condensed matter physics [1,2,3,4]
Though the quantum anomalous Hall (QAH) effect and the axion state have been discovered in TIs and magnetic topological heterostructures where ferromagnetically ordered moments are induced by chemical doping [9,10,11,12,13], an intrinsic, stoichiometric magnetic topological insulator (MTI) is highly desired in both cases, as the emerging temperatures of these macroscopic quantum states would otherwise be severely suppressed due to disorder
Apart from the possible origins of the gapless surface Dirac cone due to surface spin reorientation in ideal MnBi2Te4 single crystals, we briefly discuss the possibility of structural deformation owing to the sample imperfection that could hint at the deviation of the electronic structure between angle resolved photoemission spectroscopy (ARPES) measurements and the theoretical calculations based on A-type AFM magnetic configuration
Summary
The integration of magnetic order and topological nontriviality has received much attention since the dawn of the topological era in condensed matter physics [1,2,3,4] In these systems, the absence of time-reversal symmetry (T ) brings about a series of exotic quantum phases such as a Chern insulator [5] and axion insulator [6], leading to potential applications in the fields of spintronics and quantum computing. Though the QAH effect and the axion state have been discovered in TIs and magnetic topological heterostructures where ferromagnetically ordered moments are induced by chemical doping [9,10,11,12,13], an intrinsic, stoichiometric magnetic topological insulator (MTI) is highly desired in both cases, as the emerging temperatures of these macroscopic quantum states would otherwise be severely suppressed due to disorder
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