Title

第一原理理論計算五族和六族過渡金屬雙硫化物晶體與單原子層之自旋霍爾與自旋能斯特效應

Translated Titles

Ab initio Studies of Spin Nernst and Hall Effects in Metallic Group VB and VIB Transition Metal Dichalcogenides Bulks and Monolayers

DOI

10.6342/NTU201603838

Authors

謝政翰

Key Words

自旋電子學 ; 自旋霍爾效應 ; 自旋能斯特效應 ; 自旋軌道耦合效應 ; 過渡金屬二硫化物 ; 第一原理計算 ; Spintronics ; Spin Hall Effect ; Spin Nernst Effect ; Spin-orbit coupling ; Transition Metal Dichalcogenides ; First-principles calculations

PublicationName

臺灣大學物理學研究所學位論文

Volume or Term/Year and Month of Publication

2016年

Academic Degree Category

碩士

Advisor

郭光宇

Content Language

繁體中文

Chinese Abstract

近年來由於石墨烯的發現以及其應用上的潛力,人們對二維系統材料產生極大興趣。在此篇論文中,我們使用膺勢能及平面波方法配合貝里相位方程式對1T, 2H和1T’結構之過渡金屬二硫化物MX2 (M = Nb, Ta, V; X = S, Se, Te) 進行自旋霍爾與自旋能斯特電導率之第一原理計算。 藉由自旋霍爾與自旋能斯特效應,我們可以在不施加外加磁場與非磁性材料的情況下,自行操控電子的自旋流,這被視為自旋電子學中一相當重要之發現。2H與1T’結構之單層過渡金屬二硫化物因同時具有強自旋軌道耦合與鏡面對稱性破壞,而被預期具有良好的自旋霍爾電導率,但在我們的計算結果中,2H結構之單層過渡金屬二硫化物自旋霍爾電導率較其塊材小,而在1T’結構中,單層過渡金屬二硫化物自旋霍爾電導率與其塊材數量級相同,其中,單層之MoTe2自旋霍爾電導率較其塊材大。整體而言,2H結構之塊材TaSe2具有最大的自旋霍爾電導率,而1T’結構之單層WTe2具有最大的自旋能斯特電導率,其數量級為其餘材料的一至二個數量級。因此,我們可以發現,對於自旋電子學的研究上,而或是其應用上的價值與潛能,過渡金屬二硫化物單原子層與塊材確實是一理想的材料。

English Abstract

Recently, the two dimensional materials, such as graphene, have attracted enormous attention due to their potential applications in information technologies and the intriguing underlying physics. In this thesis, we perform a comprehensive first-principles study of spin Nernst conductivity (SNC) and spin Hall conductivity (SHC) within the Berry phase formalism based on relativistic band structure calculations for 2H-MX2 (M = Nb, Ta; X = Te, Se) and 1T’-MX2 (M = Mo, W; X = Te) bulks and monolayers. This is a vital step for spintronics that the SHE and SNE enable us to create and control spin current without magnetic field or magnetic materials. For monolayer 2H- and 1T’-MX2, they are expected to show large spin Hall conductivity for the following reasons: (i) the inversion symmetry is broken explicitly; and (ii) the spin-orbit coupling (SOC) is substantial due to the presence of heavy metal atoms. However, our computational results show that the SHC of monolayer 2H-MX2 is smaller than that of the corresponding bulk materials. In 1T’ structure, the SHC of bulks and monolayers is of the same order of magnitude, while monolayer MoTe2 shows the larger SHC compared to that of bulk. In general, bulk 2H-TaSe2 and monolayer 1T’-WTe2 show the largest SHC and SNC among our calculations. The SNC of monolayer 1T’-WTe2 is larger than that of the others by one to two orders of magnitude. Therefore, we demonstrate that the transition metal dichalcogenides (TMDCs) bulks and monolayers are truly an ideal platform for spintronics including their application purposes.

Topic Category 基礎與應用科學 > 物理
理學院 > 物理學研究所
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