Emergent Electronic Behavior of Van der Waals Heterostructures from Enforced Interlayer Coupling

非技术描述：水冷却到零度以下凝固成冰；但鲜为人知的是，即使在室温下，施加1千兆帕斯卡（GPa, = 10,000个大气压）的压力也会把水变成冰！现在，想象一下，把比固体材料高一百倍的压力施加到固体材料上：一个丰富的新现象和效应的集合将会出现，这将阐明我们对基础物理学的理解，并开发出这些材料有用的新功能。这个项目对一种特殊的材料——层状过渡金属二硫族化物——进行了实验，在这种材料中，相邻层之间的相互作用本质上是弱的，因此可以通过高压对结构和性能进行更大范围的调制。与研究工作相结合，首席研究员还开展了一项教育活动，与当地的Techbridge Girls Program合作，为访问的中学生创建一系列动手展览和实验。技术描述：在范德华（vdW）材料中，如过渡金属二硫族化合物，物理性质，如能带结构，对vdW间隙上相邻单层之间的层间耦合很敏感。如果可以人为地增强vdW材料的层间耦合，就可以有效地调制电子维度，并研究在维度调制下系统突发性物理行为的科学问题。该项目的目标是通过最大限度地调节vdW异质结构与高压的层间耦合来实现，发现和理解vdW异质结构的紧急电子行为。这些目标是通过利用金刚石砧细胞对vdW异质结构施加高达60gpa的静水压力，并探测其振动、光学和输运性质来实现的。人们预测在这种极端条件下会出现奇异的新现象，但没有经过实验测试，或者只在热能不足以破坏层间耦合的极低温度下进行了测试。在这个项目中，首席研究员和他的团队通过大幅提高vdW结构中的层间耦合能来测试和探索这些预测，以便这些效应即使在室温下也能稳定。这项研究有望在前所未有的条件下为vdW材料的性能带来新的知识，并将层状材料的功能推向现有设施之外。

Non-technical description: Water solidifies into ice when it is cooled below zero degree centigrade; but what is less known is that even at room temperature, application of a pressure of one GigaPascal (GPa, = 10,000 atmosphere) would drive water into ice! Now, imagine applying pressures up to a hundred times higher than that to solid materials: a rich collection of new phenomena and effects would emerge, which would shed light on our understanding of basic physics and development of useful new functionalities of these materials. This project does this on a special class of materials, layered transition metal dichalcogenides, where the interactions between neighboring layers are intrinsically weak, hence allowing an even wider range of modulation of the structure and properties by the high pressure. Integrated with the research effort, the principal investigator also runs an educational activity to create a series of hands-on exhibits and experiments for visits of middle-high school students in partnership with the local Techbridge Girls Program.Technical description: In van der Waals (vdW) materials such as transition metal dichalcogenides, physical properties such as band structures are sensitive to interlayer coupling between neighboring monolayers across the vdW gap. If the interlayer coupling of vdW materials can be artificially enhanced, one can effectively modulate the electronic dimensionality, and study scientific problems of emergent physical behavior of the system under the dimensionality modulation that would not arise otherwise. The goals of this project are to enable, discover and understand emergent electronic behavior of vdW heterostructures by maximally modulating their interlayer coupling with high pressures. These goals are achieved by utilizing diamond anvil cells to apply hydrostatic pressures up to 60 GPa onto vdW heterostructures, and probing their vibrational, optical and transport properties. Exotic new phenomena have been predicted to emerge at such extreme conditions, but have not been experimentally tested or were tested only at very low temperatures where the thermal energy is insufficient to destroy the interlayer coupling. In this project, the principal investigator and his team test and probe these predictions by drastically enhancing the interlayer coupling energy in the vdW structures such that these effects could be stabilized even at room temperature. The research is expected to bring new knowledge on vdW materials behaviour under unprecedented conditions and to push the boundary of layered materials functionality beyond current establishments.