Periodic Reporting for period 1 - UCoCo (Ultrafast Control of Interlayer Coupling of Two-Dimensional Layered Materials)
Reporting period: 2023-01-01 to 2024-12-31
Layered two-dimensional (2D) materials have a unique crystal structure where a two-dimensional layer of only a few-atom thickness is stacked and bound by a weak force. Nowadays, the on-demand control of layer stacking is possible. For example, we can make an isolated single-atomic layer, few-layer stacking, artificial stacking of different 2D materials, and twisted stacking of the layers. The control of layer stacking causes various exotic phenomena in 2D materials, including quantum phenomena such as superconductivity.
The interaction between the stacked 2D layers - the interlayer coupling - is the origin of the rich physics of 2D materials. 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. It is the key mechanism of the next-generation electronics and electro-optics based on 2D-material devices.
So far, the interlayer-coupling control by the electric field has been achieved by electric-circuit-based devices. Their modulation speed was limited to the microwave frequency range due to the speed of the circuit. Therefore, interlayer-coupling control of the ultrafast time scale of sub-picosecond and terahertz (THz) frequency range had never been achieved. Such ultrafast control is needed for future ultrafast devices as well as the creation of new quantum phases of 2D materials.
The interaction between the stacked 2D layers - the interlayer coupling - is the origin of the rich physics of 2D materials. 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. It is the key mechanism of the next-generation electronics and electro-optics based on 2D-material devices.
So far, the interlayer-coupling control by the electric field has been achieved by electric-circuit-based devices. Their modulation speed was limited to the microwave frequency range due to the speed of the circuit. Therefore, interlayer-coupling control of the ultrafast time scale of sub-picosecond and terahertz (THz) frequency range had never been achieved. Such ultrafast control is needed for future ultrafast devices as well as the creation of new quantum phases of 2D materials.
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."
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."
As described in "Work performed and main achievements" in detail, we have developed a novel device, a 2D-3D hybrid THz antenna, which enables the application of strong out-of-plane THz field onto 2D materials and ultrafast control over their material properties. This antenna structure has various applications in technology and fundamental science. It can bring the speed limit of the 2D field-effect transistors and 2D optical modulators, currently limited to the gigahertz frequency range, to the terahertz range. Also, it enables ultrafast control of exotic phenomena in 2D materials, such as superconductivity, interlayer exciton, and layer breathing phonon, which may lead to findings of other new states of materials.
Therefore, researchers in various fields, such as FET technology and strongly correlated material science, are expected to conduct further studies.
Therefore, researchers in various fields, such as FET technology and strongly correlated material science, are expected to conduct further studies.