课题组博士生谢兴同学在国际纳米权威期刊Nano Letters上发表论文

      近日，课题组成员谢兴同学在刘老师的指导下，以第一作者在国际纳米权威期刊《纳米快报》(Nano Letters，影响因子12.94)上发表题为 “Emergence of Optical Anisotropy in Moiré Superlattice via Heterointerface Engineering”(异质界面工程在莫尔超晶格中产生光学各向异性的研究)的实验论文。

图：异质界面工程在莫尔超晶格中产生光学各向异性的研究

        近年来，异质结构工程的研究取得了显著进展，展示了在具有高旋转对称性的单层TMDs(过渡金属二硫属化合物)中引发光学各向异性的能力。TMD层与低对称性二维材料之间的界面效应破坏了TMDs的C₃旋转对称性，导致各向异性的莫尔势和随后的光学各向异性特性。例如，Akamatsu等人在WSe₂/BP(黑磷)异质结构中通过工程实现了面内电子极化，导致了自发光伏效应。Li等人通过异质界面工程获得了MoS₂的各向异性PL(光致发光)、二次谐波生成(SHG)和导电性。最近，使用一种通用的异质界面工程策略，在低对称性面内各向异性SiP材料中，实现了单层WSe₂的Berry曲率偶极，这表明在TMDCs(过渡金属二硫属化合物)/SiP异质结构形成过程中打破TMDCs对称性是一种有效手段。这成为调控莫尔超晶格光学偏振态的理想策略和材料，同时保持了激子发射状态。

      在本研究中，我们制造了由转角角度为1.4°的WSe₂/WSe₂同质双层(THS)构成的异质结构样品，放置在低对称性SiP薄片上。偏振分辨PL光谱显示，THS的激子发射具有显著的线性偏振行为，莫尔间接激子的线性偏振度约为71%。第一性原理计算表明，这种各向异性的光学行为源于空间非均匀的电荷分布。这些光学各向异性特性可以受到温度的影响。此外，我们展示了使用磁场调制线性偏振态，揭示了激子和中性激子的偏振方向旋转角度增加以及线性偏振度相反变化的现象，这归因于在磁场下谷相干性和莫尔势的变化。这些发现强调了异质界面工程在调控莫尔超晶格光学偏振态方面的有效性。

文章链接：https://pubs.acs.org/doi/full/10.1021/acs.nanolett.4c01327

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The paper "Emergence of Optical Anisotropy in Moiré Superlattice via Heterointerface Engineering" presents significant advancements in the understanding and manipulation of optical properties in moiré superlattices. The interaction between light and these engineered superlattices offers a rich platform for exploring unique light-matter phenomena. This work highlights the immense potential of tailoring optical properties to advance the applications of moiré superlattices in fields such as photonics, optoelectronics, and valleytronics.

By constructing twisted WSe₂/WSe₂/SiP heterostructures, the authors report a remarkable linear polarization degree of approximately 70% for moiré excitons. This is attributed to the spatially non-uniform charge distribution, as confirmed by first-principles calculations. Additionally, the study demonstrates the modulation of the linear polarization state through the application of a magnetic field, resulting in polarization angle rotation and a magnetic-field-dependent linear polarization degree. These changes are influenced by valley coherence and moiré potential effects.

The findings underscore an efficient strategy for tuning the optical polarization state of moiré superlattices using heterointerface engineering, providing a pathway for further exploration and utilization in advanced optoelectronic applications. This work not only advances our fundamental understanding of moiré superlattices but also opens new avenues for their practical implementation in next-generation technologies.