Layer Decoupling in Twisted Bilayer WSe$_2$ Uncovered by Automated Dark-Field Tomography
Abstract
Twisted bilayer systems host a wealth of emergent phenomena, such as flat-band superconductivity, ferromagnetism, and ferroelectricity, arising from moir\'e superlattices and unconventional interlayer coupling. Despite their central role, direct and quantitative access to the out-of-plane atomic structure in these systems has remained elusive due to their nanoscale dimensions. Here, we introduce an automated dark-field electron tomography technique that enables three-dimensional structural analysis of atomically thin materials with sub-angstrom precision. Applying this method to twisted bilayer WSe, we uncover a significant expansion of the interlayer spacing compared to the bulk configuration, exceeding 0.1 angstrom, along with a remarkable temperature-driven interlayer decoupling unique to the twisted bilayer. Ultrafast measurement further reveals optically induced interlayer separation of ~0.2 angstrom on the picosecond timescale, attributed to transient exciton formation. These findings not only establish a powerful approach for visualizing hidden out-of-plane structures in atomically thin micro-flake materials, but also uncover the intrinsic fragility and dynamical tunability of interlayer coupling in moir\'e-engineered 2-dimensional materials.
Keywords
Cite
@article{arxiv.2601.13620,
title = {Layer Decoupling in Twisted Bilayer WSe$_2$ Uncovered by Automated Dark-Field Tomography},
author = {A. Nakamura and Y. Chiashi and T. Shimojima and Y. Tanaka and S. Akatsuka and M. Sakano and S. Masubuchi and T. Machida and K. Watanabe and T. Taniguchi and K. Ishizaka},
journal= {arXiv preprint arXiv:2601.13620},
year = {2026}
}