二維材料新視野－－能谷電子學

Review of two-dimensional valleytronics for novel technology

能谷電子學開啟了近期二維材料研究的嶄新篇章，單層過渡金屬二硫化物具有自旋-能谷偶合的特性，而有一特殊的自旋能谷在動量空間中分離，倘若能使能谷極化便能使其產生有如記憶體的二象性，可作為新世代記憶體的理想系統。本文主要回顧近年來常用於產生能谷極化的幾個經典研究，包含使用圓極化光激發能谷中載子的物理光學法、給予垂直磁場的塞曼效應和磁性材料的磁鄰近效應、電性上利用鐵磁半導體的自旋注射，和雙層TMD的錯位堆疊。最後，我們也報導了如何利用反鐵磁材料氧化鎳的磁鄰近效應來誘發MoS2的能谷極化，在此報導中我們提出了利用反鐵磁的未補償面，可以使其具有類鐵磁的特性同時保留了反鐵磁的性質，使反鐵磁與二維材料的異質結構有機會在先進記憶體技術中占有重要的一席之地。

Valleytronics of two-dimensional (2D) materials has currently sparked wide interests thanks to its non-trivial spin and valley degree of freedom coupled in the momentum space of the 2D crystal. Transition-metal-dichalcogenide (TMD) is one of the model systems for studying valleytronics and the way of how to induce valley spin-polarization, including optical alleytronics of two-dimensional (2D) materials has currently sparked wide interests thanks to its non-trivial spin and valley degree of freedom coupled in the momentum space of the 2D crystal. Transition-metal-dichalcogenide (TMD) is one of the model systems for studying valleytronics and the way of how to induce valley spin-polarization, including optical pumping using circularly polarized light, Zéeman effect induced by magnetic field, proximity effect of magnetic materials, spin injection, and the band misalignment of the 2D heterostructure. A special topic will be put on our current study of using an antiferromagnet, whose spins coupled antiparallel, to trigger a proximity effect in single-layered MoS2 so the valley spin-polarization is observed via spin-resolved photoluminescence (SR-PL) spectroscopy. The result suggests the antiferromagnet exchange-coupled with MoS2 single layer may participate in the advanced memory technology in the future.