隨著數據傳輸與高性能計算需求的快速增長，電晶體的微型化已接近物理極限，促使研究人員探索替代材料與元件架構，以延續摩爾定律的發展。過渡金屬二硫化物（TMDs）因其獨特的能谷自由度以及自旋-能谷耦合特性，成為下一代能谷電子學元件應用的潛在材料。然而，過去使用Ga(Mn)As與鐵鎳合金等鐵磁材料與TMDs整合以實現自旋注入的嘗試面臨諸多挑戰。這些方法通常需要高強度的外加磁場或複雜的材料生長過程，限制了其實際應用，進一步凸顯開發具備高效自旋注入且製程簡單的新型材料與物理架構的必要性。
本研究論文開發了一種基於凡德瓦爾異質結構的能谷電子元件，結合了單層WSe2、二維鐵磁材料Fe3GeTe2（FGT）以及超薄六方氮化硼（hBN）。透過施加偏壓，成功從FGT/hBN鐵磁穿隧電極向WSe2注入自旋極化的電洞，從而在±K谷之間產生能谷極化現象。這一現象經由圓偏振依賴的電致發光（EL）測量得到實驗驗證，並通過密度泛函理論（DFT）計算提供理論支持。此外，在外加磁場的條件下，EL的圓偏振性顯示出與FGT磁滯一致的磁滯曲線，該現象經由反射磁圓二色性（RMCD）進行驗證。研究結果表明，透過調控FGT的磁化方向，可實現可逆的自旋極化，展現其在精確自旋操控上的潛力。
FGT的高自旋極化與卓越磁性特性結合hBN的自旋保護特性，使該元件能夠實現高效自旋注入，同時避免了傳統異質結構中常見的晶格失配問題。而凡德瓦爾材料的應用則大幅簡化製程步驟，為構建高效且實用的能谷電子元件提供了一種全新的解決方案。

The rapid growth in data transmission and high-performance computing demands has pushed transistor miniaturization to its physical limits, prompting the exploration of alternative materials and architectures to extend Moore's Law. Transition metal dichalcogenides (TMDs), with their unique valley degree of freedom and strong spin-valley coupling, have emerged as promising candidates for next-generation valleytronic devices. However, previous efforts to integrate ferromagnetic materials, such as Ga(Mn)As and permalloy, with TMDs for spin injection have faced significant challenges. These approaches often require either strong external magnetic fields or complex epitaxial growth processes, thereby constraining their applicability. This highlights the need for alternative materials and device architectures that enable efficient spin injection with simplified fabrication.
In this study, we report the development of a van der Waals (vdW) heterostructure valleytronic device, combining monolayer WSe2, the two-dimensional ferromagnetic material Fe3GeTe2 (FGT), and an ultra-thin hexagonal boron nitride (hBN) spin tunnel barrier. By applying a bias voltage, spin-polarized holes are successfully injected from the FGT/hBN contact into WSe2, resulting in a population imbalance between the K and -K valleys. The valley polarization was confirmed through helicity-dependent electroluminescence (EL) measurements and supported by density functional theory (DFT) calculations. Moreover, under an external magnetic field, the EL helicity demonstrates a hysteresis loop consistent with the magnetic hysteresis of FGT, as characterized by reflective magnetic circular dichroism (RMCD). These results demonstrate the reversible spin helicity achieved by tuning the magnetization direction of FGT, underscoring its potential for precise spin manipulation.
The combination of FGT's high spin polarization and magnetic properties with the spin-preserving characteristics of hBN enables efficient spin injection while avoiding the lattice mismatch issues commonly encountered in traditional heterostructures. Furthermore, the application of van der Waals materials significantly simplifies fabrication processes, offering a novel solution for constructing efficient and practical valleytronic devices.

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