電子在拓樸絕緣體的傳輸現象

在強自旋軌道耦合下，新的絕緣態-拓樸絕緣體被發現。拓樸絕緣體的體態(bulk state)是絕緣體，但是邊界態(surface state)卻是自旋相依的導體。利用非平衡格林函數的方法結合Landauer setup，本論文將探討自旋相依的電子傳輸在拓樸絕緣體內的現象。由於材料本身所具備的新穎的特性，拓樸絕緣體被視為新一代自旋電子元件及量子電腦的熱門候選材料。長久以來，人們相信在時間反衍的保護下，縱使加了非磁性雜值拓樸絕緣體的邊界電子傳輸是完美不會被散射的。但是有理論分析發現，摻雜非磁性雜值有可能打開邊界態的能帶，進一步破壞完美傳輸。論文的第一部份我們將探討這兩個矛盾的看法，並且應用Landauer-Keldysh方程探討二維拓樸絕緣體在單雜質下的傳輸性質。第二部分，有別於第一部分，將探討是否能利用交流電極打開三維拓樸絕緣體表面態的Dirac cone。先前有實驗利用磁性雜質打開Dirac cone，但參雜的方法打開Dirac cone是不可逆的。因此，第二部分將利用Landauer-Keldysh方程結合Floquet理論研究交流電極對Dirac cone的影響。希冀，這兩部分的結果可以讓我們進一步的了解拓樸絕緣體的特性。

關鍵字

拓樸絕緣體；量子傳輸；介觀物理

並列摘要

Under the effect of strong spin-orbit coupling, the new insulator state is found and given the name ``topological insulator,' which is insulator in the bulk but conductor on the surface. The spin-dependent transport phenomena are analysed by the Landauer-Keldysh formalism, based on nonequilibrium-Green-function technique applied to the Landauer setup. Due to its fantastic properties, such as single Dirac cone, momentum-spin locking, and so on, the topological insulator has been regarded as one of the new generation candidates for spintronics devices and quantum computer. It is believed that electron transport along the edge of $2D$ or on the surface of $3D$ can not be backscattered even with non-magnetic impurity. Although this phenomenon is protected by time reversal symmetry, some analyses find that bound states are formed and open a band gap to allow backscattering. The contradiction would be studied by the powerful Landauer-Keldysh formalism. Whether periodic-alternating electrodes could open the Dirac point of the topological insulator or not is another interesting issue. There are experiments showing that the magnetic doping can open the Dirac point but the doping is irreversible, instead of electric field which is tuned externally and reversible. The combination of the Landauer-Keldysh formalism and Floquet theory facilitates the transport phenomena under the electric field periodically. These results would give us more understanding about topological insulator.

並列關鍵字

Topological Insulator ； Quantum Transport ； Mesoscopic Physics

參考文獻

Qi, S. K. Mo, R. G. Moore, D. H. Lu, M. Hashimoto, T. Sasagawa, S. C. Zhang,

formalisms for quantum transport driven by time-periodic fields. Phys. Rev. B,

[2] D. D. Awschalom and M. E. Flatte. Challenges for semiconductor spintronics. Nat

[3] B. A. Bernevig, T. L. Hughes, and S.-C. Zhang. Quantum spin hall effect and

topological phase transition in hgte quantum wells. Science, 314(5806):1757–1761,

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電子在拓樸絕緣體的傳輸現象

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