轉角電子學，藉由旋轉堆疊凡得瓦材料這項全新的技術，為操控材料能帶結構及相關物理性質提供了一個除了自旋(spin)、能谷(valley)以外的可能性。科學家利用這項技術，在小旋轉角的雙層石墨烯異質結構中發現了幾項突破性的現象，例如：超導性、非尋常的絕緣性、鐵磁性等。在大旋轉角的部分，也觀測到層與層間交互作用改變導致的狄拉克錐上升，並看到了額外簡併態的量子霍爾效應。為了研究電子在大旋轉角區域以及單、雙層交界處的傳輸特性，我們開發了一個可以在同一塊樣品上具有單、雙層石墨烯兩區域的技術。我們發現在大旋轉角所產生的不相稱區域存在著電子電洞的量子化不對稱性以及非傳統的量子霍爾效應。在這個區域中，電子端擁有八重簡併態，然而，電洞端卻是十二重簡併態，與以往的量子化現象非常的不同。除此之外，我們也在特定的載子濃度下量測到朗道能階的位移。最後，我們利用橫向電子聚焦的技術，看到解析度較低的電子訊號。從實驗結果顯示，這些特殊現象可能與大旋轉角度之雙層石墨烯的能帶結構有高度相關，而這些結果也將有機會為這個領域的探索鋪上一條康莊大道。

The brand-new fabrication tech, twisting assembly for van der Waals structures, offers an extra dimension to manipulate the band structures and associated physical properties, and leads to a novel research field named twistronics. By use of twistronic technique to enter the small twist angle regime, van der Waals heterostructures, especially the twisted bilayer graphene (tBLG) system, have demonstrated several remarkable electronic phenomena, such as the superconductivity, nontrivial insulating behaviors and ferromagnetism. On the other hand, in the large twist angle regime, the lifting of Dirac cones with two layers in the momentum space results in layer polarization, and manifest unusual degeneracy of the quantum Hall effect (QHE). In order to study the decoupling features in tBLG with a large twisting angle, as well as the junction between monolayer and such tBLG, we developed a design containing these two regimes in a single device, and report the unusual QHE and electron-hole quantization asymmetry. The transport properties of Landau quantization, in the electron side exhibits 8-fold degeneracy as a conventional Landau quantization for two decoupled sheets of graphene, whereas the 12-fold degeneracy observed on the hole side is unique from all the previously reported QHE. Also, the QH sequence appears a transition under certain carrier densities. In addition, we investigate the junction transport properties by using the transverse magnetic focusing (TMF), and observe an ambiguous focusing peak. Our results suggests that the observed phenomena may be a consequence of nontrivial band structure and require further theoretical investigations in the large-twist-angle-bilayer graphene.

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