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1. Correlated states controlled by a tunable van Hove singularity in moiré WSe2 bilayers

   https://doi.org/10.1038/s41467-025-57235-5  

   Knüppel, Patrick; Zhu, Jiacheng; Xia, Yiyu; Xia, Zhengchao; Han, Zhongdong; Zeng, Yihang; Watanabe, Kenji; Taniguchi, Takashi; Shan, Jie; Mak, Kin Fai (December 2025, Nature Communications)

   Abstract Twisted transition metal dichalcogenide (TMD) bilayers have enabled the discovery of superconductivity, ferromagnetism, correlated insulators, and a series of new topological phases of matter. However, the connection between these electronic phases of matter and the underlying band structure singularities has remained largely unexplored. Here, combining magnetic circular dichroism and exciton sensing measurements, we investigate the influence of a van Hove singularity (vHS) on the correlated phases in bilayer WSe₂with twist angle between 2 and 3 degrees. By tuning the vHS across the Fermi level using electric and magnetic fields, we observe Stoner ferromagnetism below moiré lattice filling one and Chern insulators at filling one. The experimental observations are supported by the continuum model band structure calculations. Our results highlight the prospect of engineering electronic phases of matter in moiré materials by tunable van Hove singularities. 

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2. Observation of stacking engineered magnetic phase transitions within moiré supercells of twisted van der Waals magnets

   https://doi.org/10.1038/s41467-024-49942-2  

   Li, Senlei; Sun, Zeliang; McLaughlin, Nathan J; Sharmin, Afsana; Agarwal, Nishkarsh; Huang, Mengqi; Sung, Suk Hyun; Lu, Hanyi; Yan, Shaohua; Lei, Hechang; et al (December 2024, Nature Communications)

   Abstract Recent demonstrations of moiré magnetism, featuring exotic phases with noncollinear spin order in the twisted van der Waals (vdW) magnet chromium triiodide CrI₃, have highlighted the potential of twist engineering of magnetic (vdW) materials. However, the local magnetic interactions, spin dynamics, and magnetic phase transitions within and across individual moiré supercells remain elusive. Taking advantage of a scanning single-spin magnetometry platform, here we report observation of two distinct magnetic phase transitions with separate critical temperatures within a moiré supercell of small-angle twisted double trilayer CrI₃. By measuring temperature-dependent spin fluctuations at the coexisting ferromagnetic and antiferromagnetic regions in twisted CrI₃, we explicitly show that the Curie temperature of the ferromagnetic state is higher than the Néel temperature of the antiferromagnetic one by ~10 K. Our mean-field calculations attribute such a spatial and thermodynamic phase separation to the stacking order modulated interlayer exchange coupling at the twisted interface of moiré superlattices. 

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3. Atom-by-atom imaging of moiré phasons with electron ptychography

   https://doi.org/10.1126/science.adw7751  

   Zhang, Yichao; Ahammed, Ballal; Bae, Sang Hyun; Lee, Chia-Hao; Huang, Jeffrey; Hossain, Mohammad Abir; Rakib, Tawfiqur; van_der_Zande, Arend M; Ertekin, Elif; Huang, Pinshane Y (July 2025, Science)

   Twisted two-dimensional materials exhibit distinctive vibrational modes called moiré phonons, which arise from the moiré superlattice. Here, we demonstrate atom-by-atom imaging of phasons, an ultrasoft class of moiré phonons in twisted bilayer tungsten diselenide (WSe₂). Using ultrahigh-resolution (<15 picometers) electron ptychography, we imaged the size and shape of each atom to extract time-averaged vibrational amplitudes as a function of twist angle and position. We observed several signature properties of moiré phasons, such as increased vibrational amplitudes at solitons and AA-stacked regions. By correlating experiments with molecular dynamics simulations and lattice dynamics calculations, we show that phasons dominate the thermal vibrations in low-angle twisted bilayers. These results represent a powerful route to image thermal vibrations at atomic resolution, unlocking experimental studies of a thus far hidden branch of moiré phonon physics. 

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4. Local spectroscopy of a gate-switchable moiré quantum anomalous Hall insulator

   https://doi.org/10.1038/s41467-023-39110-3  

   Zhang, Canxun; Zhu, Tiancong; Soejima, Tomohiro; Kahn, Salman; Watanabe, Kenji; Taniguchi, Takashi; Zettl, Alex; Wang, Feng; Zaletel, Michael P.; Crommie, Michael F. (December 2023, Nature Communications)

   In recent years, correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have all been observed in several moiré heterostructures. However, understanding of the physical mechanisms behind these phenomena is hampered by the lack of local electronic structure data. Here, we use scanning tunnelling microscopy and spectroscopy to demonstrate how the interplay between correlation, topology, and local atomic structure determines the behaviour of electron-doped twisted monolayer–bilayer graphene. Through gate- and magnetic field-dependent measurements, we observe local spectroscopic signatures indicating a quantum anomalous Hall insulating state with a total Chern number of ±2 at a doping level of three electrons per moiré unit cell. We show that the sign of the Chern number and associated magnetism can be electrostatically switched only over a limited range of twist angle and sample hetero-strain values. This results from a competition between the orbital magnetization of filled bulk bands and chiral edge states, which is sensitive to strain-induced distortions in the moiré superlattice. 

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5. Determining the twist angle of stacked MoS ₂ layers using machine learning‐assisted low‐frequency interlayer Raman fingerprints

   https://doi.org/10.1002/jrs.6577  

   Tang, Jing; Wang, Zifan; Tan, Qishuo; Cao, Jun; Ling, Xi (September 2023, Journal of Raman Spectroscopy)

   Abstract The investigation of twisted stacked few‐layer MoS₂has revealed novel electronic, optical, and vibrational properties over an extended period. For the successful integration of twisted stacked few‐layer MoS₂into a wide range of applications, it is crucial to employ a noninvasive, versatile technique for characterizing the layered architecture of these complex structures. In this work, we introduce a machine learning‐assisted low‐frequency Raman spectroscopy method to characterize the twist angle of few‐layer stacked MoS₂samples. A feedforward neural network (FNN) is utilized to analyze the low‐frequency breathing mode as a function of the twist angle. Moreover, using finite difference method (FDM) and density functional theory (DFT) calculations, we show that the low‐frequency Raman spectra of MoS₂are mainly influenced by the effect of the nearest and second nearest layers. A new improved linear chain model (TA‐LCM) with taking the twist angle into the consideration is developed to understand the interlayer breathing modes of stacked few‐layer MoS₂. This approach can be extended to other 2D materials systems and provides an intelligent way to investigate naturally stacked and twisted interlayer interactions. 

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