Two-dimensional transition-metal dichalcogenides such as WS 2 host tightly bound excitons because quantum confinement is strong and dielectric screening is weak. These properties make the materials useful for exploring Coulomb interactions and nonequilibrium many-body physics. In bilayers, another control knob becomes available: the relative twist angle between the two atomic sheets changes their stacking arrangement and interlayer coupling. At the same time, intense optical excitation creates carriers that dynamically screen Coulomb interactions, reducing exciton binding energy and renormalizing the quasiparticle bandgap.
A research team at Northeast Normal University has now combined these two control mechanisms in twisted bilayer WS 2 . The study, published online as a Just Accepted article in Nano Research on August 10, 2026, shows that twist angle can systematically regulate exciton binding energy, bandgap renormalization, recombination and transport. The team used polarization-resolved second-harmonic generation to determine the twist angle, Raman and photoluminescence spectroscopy to track interlayer coupling, femtosecond transient absorption spectroscopy to probe high-density exciton physics, and transient absorption microscopy to measure exciton diffusion.
The measurements revealed that the A-exciton binding energy increases from 265 meV at 0 degrees to 336 meV near 30 degrees. Near 0 degrees, stronger interlayer coupling promotes delocalization of the exciton wavefunction and enhances interlayer screening, weakening the electron–hole attraction. As the twist angle approaches 30 degrees, the interlayer interaction becomes weaker, background screening is reduced, and the exciton binding energy rises.
At higher excitation densities, photogenerated carriers strongly modify the Coulomb potential. Near the Mott transition, where excitons dissociate into an electron–hole plasma, the researchers identified the renormalized band edge from a low-energy population-inversion feature in the transient absorption spectra. The resulting bandgap renormalization ranges from 645 to 751 meV across the measured twist angles, a variation of more than 100 meV. The renormalization is strongest near 30 degrees, where weaker initial screening allows carrier-induced exchange and correlation effects to become more pronounced.
“The key result is that structural control by twist angle and ultrafast optical control by photocarriers do not act independently; together they reshape the Coulomb landscape experienced by excitons,” said Yuanzheng Li, a corresponding author of the study. “This gives a unified way to understand how exciton binding, quasiparticle bandgap renormalization and transport evolve in the same bilayer system.”
Twist angle also changes how excitons move and recombine. In the strongly coupled 0-degree bilayer, reduced electron–hole wavefunction overlap suppresses recombination and the slow lifetime component reaches 103 ps. Transient absorption microscopy further shows an effective exciton transport mobility of 134 cm²/(V·s), compared with 40 cm²/(V·s) for the 28-degree bilayer. This approximately threefold enhancement links interlayer hybridization directly to exciton transport.
The work provides a framework for designing excitonic and ultrafast optoelectronic systems in which structural geometry and photoinduced screening are used together. Rather than demonstrating a specific device, the study establishes experimentally accessible design principles for controlling high-density many-body states in layered semiconductors.
The authors are Yongsheng Gao, Jiali Chen, Yuanzheng Li, Chuxin Yan, Qingbin Wang, Wei Xin, Weizhen Liu, Haiyang Xu and Yichun Liu. Yongsheng Gao and Jiali Chen contributed equally to the work. The research was supported by the National Key R&D Program of China (No. 2023YFB3610200), the National Natural Science Foundation of China (Nos. 12474421, 62574038, 62275045 and 12274065), the Science and Technology Development Plan Project of Jilin Province, China (Nos. 20260101043JJ and 20240601049RC), and the Fund from Jilin Province (Nos. JJKH20262151BS and JJKH20250473KJ).
About the Research Team
The study was carried out by researchers at the State Key Laboratory of Integrated Optoelectronics and the Key Laboratory of UV Light-Emitting Materials and Technology of the Ministry of Education, Northeast Normal University, Changchun, China. In this work, the team combined steady-state optical spectroscopy, femtosecond transient absorption spectroscopy and transient absorption microscopy to investigate interlayer coupling, excitonic many-body interactions and ultrafast transport in two-dimensional van der Waals semiconductors.
DOI Link:
https://doi.org/10.26599/NR.2026.94909103
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
Nano Research
Twist angle controls many-body exciton physics in bilayer WS2
10-Aug-2026