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 “Pressure-Enhanced Interlayer Coupling and Hybridized Excitons in Twisted MoS₂ Moiré Quasicrystals”(扭转 MoS₂ 莫尔准晶中压力增强的层间耦合与杂化激子的特性)的实验论文。

图：扭转 MoS₂莫尔准晶中压力增强的层间耦合与杂化激子的特性

      在范德华材料中引入扭转角会形成周期性的干涉图案，即所谓的莫尔图案，它能够深刻地调控材料的电子、光学及振动性质。这些莫尔超晶格催生了在单层材料中不存在的物理现象，例如强关联电子态、拓扑相、超导性、以及电子平带结构，在基础研究与应用物理领域引发了广泛关注。当扭转角达到30°时，平移对称性被打破，仅保留十二重旋转对称性，从而形成一种被称为“莫尔准晶”的独特结构。与传统的莫尔晶体不同，莫尔准晶不具备周期性的电子排列，因而展现出独特的物理特性。研究人员已在石墨烯与TMDs的莫尔准晶中通过Umklapp散射观察到十二重电子衍射图样，这一过程可导致电子和谷自由度的耦合。在这类体系中，层间耦合起着关键作用，而调控该耦合被认为是调节莫尔准晶物理性质的有效路径。

     高压已被证明是一种调控层间耦合、从而控制扭转范德华材料中电子结构和莫尔势场的强有力工具。在施加压力下，非魔角扭转石墨烯的能带结构趋于平坦，使系统从常规态转变为强关联态。此外，在扭转TMD异质双层中，压力增强了莫尔声子的拉曼强度，展示了其调控小能带结构的潜力。这表明，高压有望成为调控莫尔准晶独特物性的有效手段，而这一方向尚未被深入探索。

     在本研究中，我们利用金刚石对顶砧(DAC)技术，研究了30° MoS₂莫尔准晶的高压光学性质。莫尔准晶的拉曼光谱显示，其莫尔声子出现于高于本征A₁g(面外振动)模的位置，且在压力升高时呈现非线性红移。随着压力增强，莫尔势场被进一步放大，导致莫尔声子与A₁g模逐渐分离，并在5 GPa以上形成稳定的频率间隙。通过比较温度与压力对莫尔声子行为的影响，我们发现压力在调控莫尔势方面更为高效。此外，压力增强的层间耦合引发了莫尔准晶主要激子峰的非单调移动，我们将其归因于片内激子与杂化层间激子的混合。进一步的声子谱与能带结构计算揭示了莫尔声子与激子在高压下的响应机制。该研究突显了高压技术在探索与调控莫尔准晶物理性质方面的实用性，进一步加深了我们对这一类新颖系统的理解。

文章链接：https://pubs.acs.org/doi/full/10.1021/acs.nanolett.5c01274

学校新闻报道：https://news.csu.edu.cn/info/1003/161531.htm

Comments:

This study presents a timely and insightful investigation into the high-pressure modulation of moiré quasicrystals, specifically focusing on 30° twisted MoS₂ bilayers. The authors effectively leverage diamond anvil cell (DAC) techniques to explore the evolution of moiré phonons and excitons under external pressure, addressing a critical gap in our understanding of how interlayer interactions influence the optical and vibrational properties of moiré quasicrystals.

One of the notable strengths of the paper lies in its demonstration that pressure-enhanced interlayer coupling not only strengthens the moiré potential but also leads to a distinct spectral separation between moiré phonons and intrinsic Raman modes. This provides compelling evidence of structural and vibrational modifications driven by external tuning. Moreover, the observation of non-monotonic exciton shifts, attributed to hybridization between intralayer and interlayer excitons, adds significant depth to our knowledge of optical transitions in quasi-periodic systems.The discussion of Umklapp scattering and intervalley coupling mechanisms, enabled by the broken translational symmetry, is particularly illuminating and helps contextualize the emergence of hybridized excitonic behavior. These findings open new avenues for exploiting pressure as a controllable parameter in moiré-engineered devices, where interlayer coupling and electronic reconstruction can be finely tuned.

Overall, this work makes a valuable contribution to the field of 2D moiré materials, especially in the largely unexplored domain of moiré quasicrystals. Future studies may further benefit from complementary temperature-dependent or ultrafast spectroscopy to decouple dynamic and static contributions to the excitonic behavior. Nonetheless, the present study convincingly establishes high-pressure spectroscopy as a powerful tool for uncovering emergent quantum phenomena in quasi-periodic van der Waals systems.