Abstract
Low-dimensional crystalline graphitic materials such as one-dimensional (1D) carbon nanotubes and two-dimensional (2D) multilayer graphene are fascinating material platforms to explore emergent physical phenomena as they feature superb material quality and are highly tunable by van der Waals interface engineering and external fields. In this talk, I will present our recent efforts to explore emergent phononic, electronic, and polarization switching in these systems. First, I will show that novel phonon modes with strongly hybridized character can arise in double walled carbon nanotubes (DWNTs) [1]. In these concentric systems, Raman-inactive acoustic phonon modes residing in different carbon shells hybridize strongly, giving rise to pronounced Raman-active modes. Next, I will demonstrate that moiré-engineered electronic insulating states with gate-tunable fillings can emerge in a 1D moiré superlattice, realized by crystallographically aligning an armchair SWNT with a two-dimensional hexagonal boron nitride (hBN) substrate [2]. In these latticealigned mixed-dimensional heterostructures, pronounced insulating states are observed at the charge neutrality point (CNP), as well as at full and half moiré fillings at low temperatures. Finally, I will present the direct imaging of electric polarization switching in tetralayer graphene, thinnest possible multilayer graphene that can host polar stacking orders [3]. This is achieved by conducting a gate-tunable scanning near-field optical microscopy (SNOM), in which we show the switching process can be realized by both electric field and mechanical force.
References:
[1] Shaoqi Sun, Qingyun Lin, Yihuan Li, Daichi Kozawa, Huizhen Wu, Shigeo Maruyama, Pilkyung Moon, Toshikaze Kariyado, Ryo Kitaura and Sihan Zhao. Strongly Hybridized Phonons in One-Dimensional van der Waals Crystals. Physical Review Letters 134, 176101 (2025)
[2] Jianfeng Bi, Masaki Minamikawa, Ruige Dong, DongJun Kang, Zihan Weng, Shaoqi Sun, Kenji Watanabe, Takashi Taniguchi, Ryosuke Okumura, Huizhen Wu, Naoto Nakatsuji, SeokJae Yoo, Mikito Koshino, Sihan Zhao. Emergent Electronic Insulating States in a One-Dimensional Moiré Superlattice. Physical Review Letters (2026) (in press) arXiv:2511.10140
[3] Zhou Zhou, Xiyao Peng, Jianfeng Bi, Fei Xue, Jie Jiang, Huizhen Wu, Zhiwen Shi, Haoliang Qian, Toshikaze Kariyado, Sihan Zhao. Imaging Electric Polarization Switching in Multilayer Graphene. Advanced Science (2026) https://doi.org/10.1002/advs.75781
Anyone interested is welcome to attend.