In this project, we aimed to enable a sub-picosecond control of the interlayer coupling of 2D materials. To investigate the ultrafast dynamics, we utilized the THz technology, which enables us to apply an extremely short pulse of an electric field - a THz pulse - to materials and observe the change of its optical properties in a sub-picosecond timescale. In the usual THz technology, however, we can apply the THz field only in the in-plane direction of the 2D material. Therefore, we developed a novel nanodevice, a 2D-3D hybrid THz antenna. It converts an incident in-plane terahertz electric field to a strong out-of-plane electric field on a layered material, enabling ultrafast control of the 2D materials.
We have designed and fabricated the 2D-3D hybrid THz antenna to apply a strong out-of-plane THz field onto a flake of a few-layer molybdenum disulfide (MoS2), an archetypal semiconductor 2D material. We have also developed a THz-pump optical-probe experiment setup to apply a strong THz pulse on the 2D-3D hybrid THz antenna and observe the ultrafast change of optical properties.
As a result of the THz-pump optical-probe experiment, we have observed an ultrafast shift of optical absorption peak energy of MoS2 in the sub-picosecond time scale. In combination with the simulation, we have clarified that the energy shift originates from the strong out-of-plane THz field caused by the 2D-3D hybrid THz antenna. It is the first control of a 2D material via an out-of-plane THz field, which opens up various technologies and science based on ultrafast control of interlayer coupling.
This result has been submitted to a peer-reviewed scientific journal, and currently under the review process. Also, we have presented this result in 2024 Annual (79th) Meeting of the Physical Society of Japan as "Material property control of molybdenum disulfide by 3D terahertz antenna."
