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

非技术描述：当水冷却到摄氏零度以下时，它就会凝固成冰；但鲜为人知的是，即使在室温下，施加10亿帕斯卡(GPA，=10000大气压)的压力也会使水结成冰！现在，想象一下，对固体材料施加高达100倍的压力：将出现丰富的新现象和新效应，这将有助于我们理解基础物理，并开发这些材料的有用新功能。该项目对一类特殊的材料--层状过渡金属二卤化物进行了研究，其中相邻层之间的相互作用本质上很弱，因此允许通过高压对结构和性能进行更广泛的调制。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，为中学生的参观创建了一系列动手展览和实验。技术描述：在范德瓦尔斯(VDW)材料中，如过渡金属二卤化物，物理性质，如能带结构，对跨越VDW间隙的相邻单层之间的层间耦合非常敏感。如果能够人为地增强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紧急物理行为的科学问题，否则就不会出现这种情况。该项目的目标是通过在高压下最大限度地调节VDW异质结的层间耦合来实现、发现和理解VDW异质结的紧急电子行为。这些目标是通过利用钻石顶压室在VDW异质结构上施加高达60 Gpa的流体静压并探测它们的振动、光学和传输特性来实现的。据预测，在这种极端条件下会出现奇异的新现象，但还没有经过实验测试，或者只在热能不足以破坏层间耦合的极低温度下进行测试。在这个项目中，首席研究员和他的团队通过大幅增强VDW结构中的层间耦合能量来测试和探索这些预测，以便即使在室温下这些效应也可以稳定下来。这项研究有望为VDW材料在前所未有的条件下的行为带来新的知识，并将分层材料功能的边界推向现有机构之外。

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.