本實驗主要是研究磁性絕緣層與拓撲絕緣體雙層結構的磁鄰近效應(Proximity effect)。首先，在實驗中會利用脈衝雷射沉積儀(PLD)與分子束磊晶系統(MBE)分別成長磁性絕緣層CoFe2O4和拓樸絕緣層Bi2Se3。實驗分成兩個部分，第一部分是藉由改Bi2Se3厚度的方式來降低Bulk載子濃度，在磁阻的量測結果觀察到weak antilocalization (WAL)被抑制的現象，且我們利用擬合HLN方程式得到α值與l_ϕ值並觀察到明顯的變化，表示Bi2Se3層有受到磁性層的磁性散射影響。第二部分則是利用Sb原子的摻雜讓Bi2Se3可以有效的降低Bulk的載子濃度，在不同的Sb摻雜比例的磁阻分析，觀察到WAL被抑制的現象更加顯著。最後我們也透過量測不同外加磁場下，分析溫度與電導的斜率，可觀察到拓樸絕緣體表面態能隙隨著外加磁場變大而變大的趨勢。

In this study, we mainly investigate the proximity effect in topological insulator and magnetic insulator bilayer system. In the experiment, Bi2Se3Sb/CoFe2O4 heterostructure was fabricated by using the molecule beam epitaxial technique and the pulsed laser deposition system, respectively. To observe the surface state of topological insulator, since we essentially need to reduce the bulk carrier concentration. In next step, a series of heterostructure magnetoresistance results are measured by PPMS. In contrast to single layer sample, Bi2Se3Sb/CFO heterostructure samples can suppress the WAL phenomenon. Then, the MR results are fitted by the modified HLN equation and successfully obtain the size of surface state gap. We can efficiently decrease the bulk carrier concentration of Bi2Se3 by doping Sb. The temperature dependent resistance of heterostructure samples at different external magnetic fields are also measured and analyzed. The results indicate the phenomenon of surface band gap opening with increasing external magnetic field.

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