The Layer-inserting Growth of Antiferromagnetic Topological Insulator MnBi${}_2$Te${}_4$ Based on Symmetry and Its X-ray Photoelectron Spectroscopy

Abstract

The antiferromagnetic topological insulator has attracted lots of attention recently, as its intrinsic magnetism and topological property makes it a potential material to realize the quantum anomalous Hall effect (QAHE) at relative high temperature. Until now, only MnBi${}_2$Te${}_4$ is predicted and grown successfully. The other MB${}_2$T${}_4$-family materials predicted (MB${}_2$T${}_4$:M=transition-metal or rare-earth element, B=Bi or Sb, T=Te, Se, or S) with not only antiferromagnetic topological property but also rich and exotic topological quantum states and dynamically stable (or metastable) structure have not been realized on experiment completely. Here, MnBi${}_2$Te${}_4$ single crystals have been grown successfully and tested. It shows typical antiferromagnetic character, with Neel temperature of 24.5K and a spin-flop transition at H$\approx$35000 Oe, 1.8K. After obtaining MnBi${}_2$Te${}_4$ single crystals, we have tried to synthesize the other members of MB${}_2$T${}_4$-family materials, but things are not going so well. Then it inspires us to discuss the growth mechanism of MnBi${}_2$Te${}_4$. The growth mode may be the layer-inserting growth mode based on symmetry, which is supported by our X-ray photoelectron spectroscopy (XPS) measurement. The XPS measurement combing with the $A{r}^{+}$ ion sputtering is done to investigate the chemical state of MnBi${}_2$Te${}_4$. Binding energies (BE) of the MnBi${}_2$Te${}_4$-related contributions to Mn2p and Te3d spectra agree well with those of inserting material $\hat{I}\pm$-MnTe. Rising intensity of the Mn2p satellite for divalent Mn (bound to chalcogen) with atomic number of ligand (from MnO to MnBi${}_2$Te${}_4$) has been observed, thus suggesting classification of MnBi${}_2$Te${}_4$ as the charge-transfer compound. Understanding the growth mode of MnBi${}_2$Te${}_4$ can help us to grow the other members of MB${}_2$T${}_4$-family materials.