磁場作用下外爾半金屬之電子傳輸性質

Electronic transport properties of Weyl semimetals under magnetic field

陳碩宏(Shuo-Hung Chen)

指導教授 ： 薛文証

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202100214

摘要

本論文旨為研究單層位障結構與雙層位障結構下，外爾半金屬之電子傳輸特性。透過改變施加的偏壓與材料的參數，包含：位障寬度比、位障高度、磁矢勢與入射能量等變化，並討論其電流以及電導大小的影響。而電流是藉由彈道傳輸所求得。本論文將使用外爾半金屬模型以及轉移矩陣法來描述外爾費米子的行為，可看出電位障並不會消除克萊恩穿隧，且費米波向量在特定位障寬度下的共振會產生完美傳輸，而磁位障則會影響此穿透圖形之對稱性。當位障高度接近入射能量時，亦可以透過磁位障來篩選特定之入射。另外，電流會隨著位障寬度比，以及費米狄拉克分布之影響，產生劇烈之變動。因此，本論文在不破壞其線性色散關係的情況下，分析傳輸特性，藉此達到實現外爾半金屬做為電子器件之構想。

關鍵字

外爾半金屬 ； 克萊恩穿隧效應 ； 轉移矩陣 ； 外爾費米子 ； 彈道傳輸 ； 手徵反常

並列摘要

The purpose of this thesis is to explore the electron transport properties of Weyl semimetal under single-layer barrier structure and double-layer barrier structure. By changing the applied bias voltage and material parameters, including: barrier width ratio, barrier height, magnetic vector potential and incident energy, etc., we discuss the influence of its current and conductance. The current is obtained by ballistic transmission. This thesis will use the Weyl semimetal model and the transfer matrix method to describe the behavior of Weyl fermions. It can be seen that the potential barrier will not eliminate Klein tunneling, and the resonance of the Fermi wave vector under a specific barrier width will produce perfect transmission, and the magnetic barrier will affect the symmetry of the transmission pattern.When the height of the barrier is close to the incident energy, the specific incident can also be filtered through the magnetic barrier. In addition, the current will change drastically with the barrier width ratio and the Fermi-Dirac distribution. Therefore, this thesis analyzes the transmission characteristics without destroying the linear dispersion relationship, so as to achieve the idea of realizing Weyl semimetal as an electronic device.

並列關鍵字

Weyl semimetal ； Klein tunneling effect ； transfer matrix ； Weyl fermion ； Ballistic transport ； Chiral anomaly

參考文獻

[1] P. Hosur and X. L. Qi, “Recent developments in transport phenomena in Weyl semimetals,” C. R. Phys. 14, 857-870 (2013).

[2] S. Y. Xu, I. Belopolski, N. Alidoust, M. Neupane, G. Bian, C. L. Zhang, R. Sankar, G. Q. Chang, Z. J. Yuan, C. C. Lee, S. M. Huang, H. Zheng, J. Ma, D. S. Sanchez, B. K. Wang, A. Bansil, F. C. Chou, P. P. Shibayev, H. Lin, S. Jia, and M. Z. Hasan, “Discovery of a Weyl fermion semimetal and topological Fermi arcs,” Science 349, 613-617 (2015).

[3] B. Q. Lv, H. M. Weng, B. B. Fu, X. P. Wang, H. Miao, J. Ma, P. Richard, X. C. Huang, L. X. Zhao, G. F. Chen, Z. Fang, X. Dai, T. Qian, and H. Ding, “Experimental discovery of Weyl semimetal TaAs,” Phys. Rev. X 5, 031013 (2015).

[4] S. M. Huang, S. Y. Xu, I. Belopolski, C. C. Lee, G. Q. Chang, B. K. Wang, N. Alidoust, G. Bian, M. Neupane, C. L. Zhang, S. Jia, A. Bansil, H. Lin, and M. Z. Hasan, “A Weyl fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class,” Nat. Commun. 6, 7373 (2015).

[5] H. M. Weng, C. Fang, Z. Fang, B. A. Bernevig, and X. Dai, “Weyl semimetal phase in noncentrosymmetric transition-metal monophosphides,” Phys. Rev. X 5, 011029 (2015).