Abstract
The intrinsic magnetic topological insulator MnBi2Te4 has attracted much attention due to its special magnetic and topological properties. To date, most reports have focused on bulk or flake samples. For material integration and device applications, the epitaxial growth of MnBi2Te4 film in nanoscale is more important but challenging. Here, we report the growth of self-regulated MnBi2Te4 films by the molecular beam epitaxy. By tuning the substrate temperature to the optimal temperature for the growth surface, the stoichiometry of MnBi2Te4 becomes sensitive to the Mn/Bi flux ratio. Excessive and deficient Mn resulted in the formation of a MnTe and Bi2Te3 phase, respectively. The magnetic measurement of the 7 SL MnBi2Te4 film probed by the superconducting quantum interference device (SQUID) shows that the antiferromagnetic order occurring at the Néel temperature 22 K is accompanied by an anomalous magnetic hysteresis loop along the c-axis. The band structure measured by angle-resolved photoemission spectroscopy (ARPES) at 80 K reveals a Dirac-like surface state, which indicates that MnBi2Te4 has topological insulator properties in the paramagnetic phase. Our work demonstrates the key growth parameters for the design and optimization of the synthesis of nanoscale MnBi2Te4 films, which are of great significance for fundamental research and device applications involving antiferromagnetic topological insulators.
Highlights
Magnetic topological insulators (TIs) are an attractive platform because their finite magnetic moment provides mass to the massless Dirac fermions, thereby opening an energy gap in an otherwise gapless Dirac state, leading to several emerging topologically driven quantum states [1,2,3]
The MnBi2 Te4 samples were grown on c-plane Al2 O3 substrates with the molecular beam epitaxy (AdNaNo Corp., model MBE-9, New Taipei, Taiwan) method in an ultrahigh vacuum (UHV) chamber equipped with reflection high-energy electron diffraction (RHEED) [39,40]
The electronic structure of 7 SL MnBi2 Te4 with growth parameters φr = 0.09 and TG = 410 ◦ C was studied with angle-resolved photoemission spectroscopy (ARPES), which were recorded at 80 K, to which the sample was paramagnetically ordered
Summary
Magnetic topological insulators (TIs) are an attractive platform because their finite magnetic moment provides mass to the massless Dirac fermions, thereby opening an energy gap in an otherwise gapless Dirac state, leading to several emerging topologically driven quantum states [1,2,3]. The fabrication of MnBi2 Te4 flakes requires heating to a high temperature, which readily causes high-density intrinsic defects Such defects in MnBi2 Te4 cause bulk metallic conductivity, preventing the measurement of the quantum transport of the surface states, but it might affect magnetic and topological properties [24,25]. The MBE growth of high-quality MnBi2 Te4 films is essential for the practical development of devices designed to exploit the remarkable properties of the QAH state and axion insulator state. This work establishes a systematic approach to the epitaxial growth of high-quality MnBi2 Te4 films for future device applications
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