Phononic and electronic transport in multilayer 2D materials via topologically protected and photo-excited states

In this presentation, we deliver two topics on theoretical/computational approaches to phononic transport and its induction of electron transfer in multilayer 2D materials. Elastic devices operating at high frequencies have been used for a number of applications, including filters in wireless telecommunication devices. Conventional elastic devices have the limitations in achieving high integration and complex functionality due to their increasing loss factors as the physical scale is reduced. To overcome this limitation, “topological phononics,” which applies the concept of band topology to acoustic dispersion, has attracted increasing attention in recent years. We have demonstrated both theoretically and experimentally that such topologically protected elastic wave control is possible in the GHz frequency range [1]. The challenge in further applying the methodology to next-generation (THz range) devices is to design topological waveguides at the nano or even atomic scales.

The first topic is a density-functional study of phonon dispersion and topological invariance in multilayer 2D (vam der Waals) materials to design theoretically the topological waveguide in the THz band. Specifically, by introducing defects and/or grain boundaries in a bilayer structure of graphene and boron nitride (BN), we show the localization of phonons as topological edge states can be excited at a specific frequency.

The second topic is a phonon-induced electron transport between carbon nanotube (CNT) and boron nitride nanotube (BNNT) in CNT/BNNT heterostructures. By ultrafast time-resolved electron diffraction measurements [2], it has been has been shown that a photo-induced charge transfers from CNT to BNNT through electron channels and that subsequently radial phonons at the interface of the heterostructure are formed. We try to elucidate this process by the ab-initio phonon calculations and demonstrate that the electron transport from CNT to BNNT can be controlled by selectively exciting an interlayer phonon mode in THz regime.

Reference:

[1] D. Hatanaka, H. Takeshita, M. Kataoka, H. Okamoto, K. Tsuruta, H. Yamaguchi, Nano Lett. 24, 5570 (2024).

[2] Y. Saida, T. Gauthier, H. Suzuki, S. Ohmura et al., Nat. Commun. 15, 4600 (2024).