Chemical Aspects of the Candidate Antiferromagnetic Topological Insulator MnBi₂Te₄

Abstract

Crystal growth of MnBi 2 Te 4 has delivered the first experimental corroboration of the 3D antiferromagnetic topological insulator state. Our present results confirm that the synthesis of MnBi 2 Te 4 can be scaled-up and strengthen it as a promising experimental platform for studies of a crossover between magnetic ordering and non-trivial topology. High-quality single crystals of MnBi 2 Te 4 are grown by slow cooling within a narrow range between the melting points of Bi 2 Te 3 (586 °C) and MnBi 2 Te 4 (600 °C). Single crystal X-ray diffraction and electron microscopy reveal ubiquitous antisite defects in both cation sites and, possibly, Mn vacancies. Powders of MnBi 2 Te 4 can be obtained at subsolidus temperatures, and a complementary thermochemical study establishes a limited high-temperature range of phase stability. Nevertheless, quenched powders are stable at room temperature and exhibit long-range antiferromagnetic ordering below 24 K. The expected Mn(II) out-of-plane magnetic state is confirmed by the magnetization, X-ray photoemission, X-ray absorption and linear dichroism data. MnBi 2 Te 4 exhibits a metallic type of resistivity in the range 4.5-300 K. The compound is an n-type conductor that reaches a thermoelectric figure of merit up to ZT = 0.17. Angle-resolved photoemission experiments provide evidence for a surface state forming a gapped Dirac cone.

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.…”

“…3). A Dirac-like TSS is observed around the Γ point of all 4 three materials (marked by the orange dashed lines in Fig. 3d,h,l).…”

“…In the newly discovered magnetic topological insulator MnBi2Te4 [1][2][3][4][5][6][7][8], both axion insulator state and quantized anomalous Hall effect (QAHE) have been observed by tuning the magnetic structure [9][10][11]. The related (MnBi2Te4)m(Bi2Te3)n heterostructures with increased tuning knobs, are predicted to be a more versatile platform for exotic topological states [12][13][14][15][16].…”

Antiferromagnetic topological insulator MnBi2Te4: synthesis and magnetic properties

“…According to previous studies, MnBi2Te4 can be synthesized through a number of approaches, but lacks of the evidence of high purity crystalline samples 29 . During the preparation of this paper, we noticed that there have been several publications concerning the growth and characterizations of MnBi2Te4 crystals 20,30,31 . However, the synthetic strategy toward high-quality millimetersized MnBi2Te4 single crystals with unambiguous AFM transition was still challenging.…”