Recently, the emerging conceptual valley-related devices have attracted much attention due to the progress on generating, controlling, and detecting the valley degree of freedom in the transition metal dichalcogenide (TMD) monolayers. In general, it is known that achieving valley degree of freedom with long valley lifetime is crucial in the implementation of valleytronic devices. Here, we provide a brief introduction of the basic understandings of valley degree of freedom. We as well review the recent experimental advancement in the modulation of valley degree of freedom. The strategies include optical/magnetic/electric field tuning, moiré patterns, plasmonic metasurface, defects and strain engineering. In addition, we summarize the corresponding mechanisms, which can help to obtain large degree of polarization and long valley lifetimes in monolayer TMDs. Based on these methods, two-dimensional valley-optoelectronic systems based on TMD heterostructures can be constructed, providing opportunities for such as the new paradigm in data processing and transmission. Challenges and perspectives on the development of valleytronics are highlighted as well.

中文翻译：

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单层过渡金属二硫化物及其混合系统中的谷操作：现状和挑战

最近，由于在过渡金属二硫属化物（TMD）单分子层中产生、控制和检测谷自由度的进展，新兴的概念谷相关器件引起了广泛关注。一般来说，众所周知，实现具有长谷寿命的谷自由度对于谷电子器件的实现至关重要。在这里，我们简要介绍一下谷自由度的基本认识。我们还回顾了最近在谷自由度调制方面的实验进展。这些策略包括光/磁场/电场调谐、莫尔图案、等离子体超表面、缺陷和应变工程。此外，我们总结了相应的机制，这有助于在单层 TMD 中获得大程度的极化和长谷寿命。基于这些方法，可以构建基于TMD异质结构的二维谷光电系统，为数据处理和传输的新范式提供机会。还强调了山谷电子学发展面临的挑战和前景。