UCoCo · Ultrafast Control of Interlayer Coupling of Two-Dimensional Layered Materials

Layered two-dimensional materials are novel quantum materials considered as the basis for future-generation electronics. The electronic and optical properties of such materials critically depend on so-called interlayer coupling – the interaction between the neighboring atomic layers within the material. What is of particular interest is that one can modulate this interlayer coupling, and thereby the material’s properties, by applying an electric field in the out-of-plane direction of the atomic layers. In this project, I focus on a typical semiconductor layered material called transition-metal dichalcogenides (TMDC). In TMDC, bandgap modulation with DC electric fields was recently achieved. However, the limitation of the modulation speed remains yet unclarified. In addition, the expected insulator-metal transition at the strong-field limit has not yet been realized because the required strong field causes a dielectric breakdown of the material.This project aims to (1) Realize ultrafast control of electronic properties of layered materials via direct ultrafast manipulation of interlayer coupling, (2) Identify the speed limitations to this controlling mechanism, and (3) Realize the insulator-metal transition in the layered material via the ultrafast control scheme. To investigate the ultrafast dynamics, I will utilize the terahertz technology, which enables us to apply a very short pulse of an electric field - a terahertz pulse - to the material and observe the change of its optical properties in an ultrafast timescale. A newly proposed micrometer-sized device, which converts an incident terahertz pulse to a strong out-of-plane electric field on TMDC, will enable ultrafast property control.The proposed scheme will be applicable for the ultrafast control of quantum phases in various layered-material systems. It is also expected to be applied as optoelectronic and all-optical ultrafast switches, which are important milestones for future ultrafast technologies.