拓樸絕緣體特殊的能帶結構導致此種材料在內部絕緣而在邊緣或表面導電，若是將磁性摻雜於拓樸絕緣體，則會破壞時間反衍對稱性(time reversal symmetry)，此時便會出現量子異常霍爾效應(Quantum Anomalous Hall Effect, QAHE)、拓樸軸子態(topological axion states)和馬約拉納費米子(Majonara fermion)這些特殊的量子態，因此磁性拓樸絕緣體為日後研究量子拓樸、電子自旋學以及其應用的重要載體，其中MnBi2Te4即是被預測為反鐵磁性拓樸絕緣體。
本實驗以分子束磊晶系統(Molecular Beam Epitaxy, MBE)成長反鐵磁性拓樸絕緣體MnBi2Te4薄膜，調整成長樣品時的參數得到結構晶向良好的樣品，並研究其物理性質。以X光繞射(X-ray Diffraction, XRD)分析樣品的晶格結構，改變成長樣品時的Mn與Bi的分壓比，以抑制雜向產生(如:MnTe)。藉由原子力顯微鏡(Atomic Force Microscope, AFM)觀察不同成長溫度的樣品表面，調整成長的基板溫度使樣品膜面平整度達到最佳，觀察到MnBi2Te4層狀堆疊的結構。利用穿透式電子顯微鏡(Transmission Electron Microscope, TEM)觀察薄膜剖面確認層狀結構和能量散佈分析儀(Energy Dispersive Spectrometer, EDS)分析薄膜樣品中的化學成分及比例。由角解析光電子能譜(Angle resolved photoemission spectroscopy, ARPES)量測MnBi2Te4的能帶結構，在價帶與導帶的能隙中發現其表面態，證實MnBi2Te4為拓樸絕緣體。
最後探討不同薄膜厚度之MnBi2Te4薄膜的磁性與電性。磁性方面，由超導量子干涉儀(Super conducting Quantum Interference Device, SQUID)量測磁化率及磁滯曲線，在低於涅爾溫度(Neel temperature)時MnBi2Te4呈現反鐵磁性，且不同薄膜厚度涅爾溫度不同。電性方面，由物理性質量測系統(Physical Properties Measurement Systems, PPMS)在低溫量測霍爾電阻Rxy及磁阻Rxx，由量測結果可知載子傳輸類型為n型載子為主，霍爾電阻與磁阻皆會因MnBi2Te4薄膜本身的反鐵磁性與外加磁場而有所變化。
關鍵字：分子束磊晶、MnBi2Te4、磁性拓樸絕緣體、角解析光電子能譜、反鐵磁性

In this study, MnBi2Te4 thin film were grown on sapphire (0001) substrate with molecular beam epitaxy (MBE) system. Tuning Mn/Bi flux ratio and growth temperature are effective to fabricate high quality and single phase of MnBi2Te4 thin film., the structural characterization of MnBi2Te4 thin film had been verified by X-ray diffraction (XRD), indicating that growth of a single crystal in the c-axis direction. Both atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) show the layered structure of MnBi2Te4 with septuple layers (SLs) structure. The band structure of MnBi2Te4 thin film investigated by angle resolved photoemission spectroscopy (ARPES) measurements shows the exist of surface state, which confirm the MnBi2Te4 thin film is a topological insulator (TI). The magnetic properties of different thickness MnBi2Te4 thin film were investigated with superconducting quantum interference device (SQUID) measurement, which reveal that MnBi2Te4 have antiferromagnetic behavior, and its Neel temperature is about 22~23K. The transport properties of MnBi2Te4 thin films were studied with physical properties measurement system (PPMS) measurement. MnBi2Te4 thin films exhibit a n-type transport behavior in the Hall effect. Understanding how to fabricate MnBi2Te4 is the key to synthesizing new TI materials with antiferromagnetic properties, which together are routes to realize and control exotic quantum phenomena.
Key words: Molecular beam epitaxy, MnBi2Te4, Topological insulator, ARPES, Antiferromagnetic

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