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

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

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.