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標題: | 第一原理計算研究外爾和狄拉克半金屬 LaAlGe 和 CuMnAs 之體光伏效應和量子幾何學 An Ab Initio Study of Bulk Photovoltaic Effect and its Quantum Geometry in Weyl and Dirac Semimetal LaAlGe and CuMnAs |
作者: | 蕭予誠 Yu-Cheng Shaw |
指導教授: | 郭光宇 Guang-Yu Guo |
關鍵字: | 外爾半金屬,狄拉克半金屬,非線性光學,體光伏效應,量子幾何量,第一原理計算, Weyl semimetal,Dirac semimetal,nonlinear optics,bulk photovoltaic effect,quantum geometry,first-principle calculation, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 由於實驗技術的進步、許多有前途的應用以及與拓撲的直接聯繫,非線性光學近年來受到廣泛關注。在非線性光學中,體光伏效應描述 了二階電場下直流電的產生。拓撲半金屬被預測具有落在太赫茲範圍內的低頻發散。這可能開啟新的應用,例如光電探測和太赫茲通信。體光伏效應也被認為是一種有效的機制,可以在均質材料中利用太陽光發電。基於這種機制的太陽能電池與傳統 p-n 接面相比具有優勢,即產生的電壓不受帶隙值的限制。理論方面也很有趣:實驗和第一原理結果證實了貝里曲率與外爾半金屬中的量子化圓偏振注入電流之間的關係。由於圓偏振注入電流只是體光伏效應中四種電流之一,其餘電流是否存在其他關係成為一個自然的問題。最近的一篇論文確實進一步指出了與所有不同類型的體光伏電流相關的其他幾何量的存在。因此在本研究中,我們選擇了兩種材料,外爾半金屬 LaAlGe 和狄拉克半金屬 CuMnAs,它們擁有所有體光伏電流及其相應的幾何量,以實現對這些現象的真實材料研究。我們利用第一原理密度泛函理論得到的科恩-沈呂九軌道計算物理量和瓦尼爾插值方程。我也嘗試找出主要貢獻的區域和可能的機制。在 LaAlGe 中計算出接近 20 (毫安/伏特平方) 的大圓偏振注入電流和高達 0.5(毫安/伏特平方) 的線性偏移電流。當局部磁矩方向從 c 軸變為 b 軸時,CuMnAs 中的線性注入電流出現張量分量的變化和清晰的峰值。我在LaAlGe、c 軸反鐵磁 CuMnAs 和 b 軸反鐵磁 CuMnAs 中系統性地研究了所有體光伏效應電導率和量子幾何量。此外,量子度規的布里淵區切片研究顯示了與輸出電流方向直接對應的有趣的不對稱行為。 Nonlinear optics (NLO) gains ample attention in recent years due to advances in experimental techniques, its many promising applications as well as its direct link to topology. Among NLO processes, bulk photovoltaic effect (BPVE) describes the generation of direct current (DC) under second-order electric field. In topological semimetals, it is predicted to have low-frequency divergence which falls within the terahertz regime. This could open new applications such as photodetection and terahertz communication. BPVE is also proposed to be an efficient mechanism to generate electricity from sunlight in a homogenous material. Solar cells based on this mechanism has the advantage over traditional p-n junction that the voltage generated is not limited by the value of bandgap. The theoretical aspect is also interesting: experimental and first principle results have confirmed the relation between Berry curvature and the quantized circular injection current in Weyl semimetals. Since the circular injection current is just one of the four currents in BPVE, it is natural to ask if there exist other relations for the remaining currents. A recent paper indeed further points out the existence of other geometric quantities related to all different kinds of BPVE current. In this study we thus choose two materials, Weyl semimetal LaAlGe and Dirac semimetal CuMnAs, that complete all the BPVE currents and their corresponding geometric quantities to realize a real material study of these phenomena. Kohn-Sham orbitals obtained by first-principle density functional theory are used to calculate physical quantities and Wannier interpolated function. I also try to find dominant regions and possible mechanisms for various quantities. A large circular injection current close to 20 (mA/V2) and linear shift current up to 0.5 (mA/V2) is calculated in LaAlGe. Component change and a clear peak emerge for the linear injection current in CuMnAs when the local magnetic moment direction is changed from c-axis to b-axis. All the BPVE conductivities and quantum geometric quantities are systematically studied in LaAlGe, c-axis AFM CuMnAs, and b-axis AFM CuMnAs. Furthermore, the k-slice study of the quantum metric shows interesting asymmetry behavior directly corresponding to the outgoing current direction. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/87067 |
DOI: | 10.6342/NTU202300381 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 物理學系 |
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