| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 104 === Because of the inversion symmetry breaking and strong spin-orbit coupling, interest in transition-metal dichalcogenides MX2 ( M = Ta, Nb, V and X = S, Se ) have emerged since the discovery of graphene. In this thesis, a systematic first principle study of spin, anomalous and valley Hall conductivities of transition metal dichalcogenides in both 1T and 2H structure is performed with full-potential projector-augmented wave method with Berry-phase formalism. The experimetal crystal structures are used.
Spin Hall effect (SHE) enables us to control spins without magnetic field or magnetic materials, which is a crucial step for spintronics. Because of the inversion symmery breaking and strong spin-orbit coupling in 2H-transition-metal dichalcogenides monolayers, charge carriers in opposite valleys carry opposite Berry curvature and spin moment, which is expected to have a good spin Hall effect and vally Hall effect. Our results show that the intrinsic spin Hall conductivity in 2H-transition-metal dichalcogenides monolayer is smaller compared to bulk. Though in 1T-structure, the intrinsic spin Hall conductivity in bulk transition-metal dichalcogenides is smaller compared to monolayer. The 1T-TaSe2 monolayer presents the largest intrinsic spin Hall conductivity and the 2H-TaSe2 monolayer exhibits the largest valley Hall conductivity and the 1T-VSe2 monolayer posseses the largest anomalous Hall conductivity. Our results demonstrate transition-metal dichalcogenides monolayers to be an ideal platform for spintronics applications.
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