Surface states and Rashba-type spin polarization in antiferromagnetic MnBi2Te4 (0001)

Abstract

The layered van der Waals antiferromagnet MnBi2Te4 has been predicted to combine the band ordering of archetypical topological insulators like Bi2Te3 with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of MnBi2Te4(0001) single crystals by use of spin-and angle-resolved photoelectron spectroscopy (ARPES) experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure.The hallmark of a topological insulator is a single spinpolarized Dirac cone at the surface which is protected by time reversal-symmetry and originates from a band inversion in the bulk [1,2]. Notably, breaking time-reversal symmetry by magnetic order does not necessarily destroy the non-trivial topology but instead may drive the system into another topological phase. One example is the quantum anomalous Hall (QAH) state that has been observed in magnetically doped topological insulators [3]. The QAH state, in turn, may form the basis for yet more exotic electronic states, such as axion insulators [4,5] and chiral Majorana fermions [6]. Another example is the antiferromagnetic topological insulator state which is protected by a combination of time-reversal and lattice translational symmetries [7].Magnetic order in a topological insulator has mainly been achieved by doping with 3d impurities [3,8], which however inevitably gives rise to increased disorder. By contrast, the layered van der Waals material MnBi 2 Te 4 [9, 10] has recently been proposed to realize an intrinsic magnetic topological insulator [11][12][13][14], i.e. a compound that features magnetic order and a topologically non-trivial bulk band structure at the arXiv:1903.11826v2 [cond-mat.str-el]

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

“…Two branches of the dispersion intersect each other at a single Dirac point, showing the gapless nature of the TSS. 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].…”

“…A universal gapless Dirac cone is observed at the MnBi2Te4 terminated (0001) surfaces in all systems. This is in sharp contrast to the expected gap from the original antiferromagnetic ground state [2][3][4]9,[17][18][19], indicating an altered magnetic structure near the surface, possibly due to the surface termination. In the meantime, the electron band dispersion of the surface states, presumably dominated by the top surface [20,21], is found to be sensitive to different stackings of the underlying MnBi2Te4 and Bi2Te3 layers.…”

Intrinsic axion insulating behavior in antiferromagnetic MnBi6Te10

“…Subsequently, single crystals of MnBi 2n Te 3n+1 were grown and physical properties, including electrical and thermal transport, magnetization, neutron scattering, etc., were measured which support possible realization of the axion insulator in these materials [16][17][18][19][20][21]. While some ARPES studies reported observation of a gapped surface state in MnBi 2n Te 3n+1 and thus possible axion insulator behavior [22][23][24][25], many others showed evidence that the surface state in this material remains gapless or diminished gap down to low temperatures [26][27][28][29][30]. The latter may be a result of weak hybridization between the magnetic states and the topological electronic states [30] or possibly a different (or disordered) magnetic structure at the top Mn-Te layer [26,28].…”

Realization of an intrinsic ferromagnetic topological state in MnBi 8 Te 13

“…Recently, MnBi 2 Te 4 , a van der Waals (vdW) compound composed of the septuple layers (SLs) of [MnBi 2 Te 4 ], was identified as an intrinsic magnetic topological material with clean band structure ( 10 – 32 ). Unfortunately, magnetic moments in MnBi 2 Te 4 are antiferromagnetically (AFM) coupled across adjacent [MnBi 2 Te 4 ] planes ( 15 , 31 ).…”