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We study the coupled charge density wave (CDW) and insulator-to-metal transitions in the 2D quantum material 1T-TaS₂. By applying in situ cryogenic 4D scanning transmission electron microscopy with in situ electrical resistance measurements, we directly visualize the CDW transition and establish that the transition is mediated by basal dislocations (stacking solitons). We find that dislocations can both nucleate and pin the transition and locally alter the transition temperatureT_cby nearly ~75 K. This finding was enabled by the application of unsupervised machine learning to cluster five-dimensional, terabyte scale datasets, which demonstrate a one-to-one correlation between resistance—a global property—and local CDW domain-dislocation dynamics, thereby linking the material microstructure to device properties. This work represents a major step toward defect-engineering of quantum materials, which will become increasingly important as we aim to utilize such materials in real devices. 

Intercalation of alkali metals is widely studied to introduce a structural phase transition from 2H to 1T′ in 2D group VI transition metal dichalcogenides (TMDCs). This highly efficient phase transition method has enabled an access to a library of phases with novel physical and chemical properties attractive for functional devices and electrochemical catalysis. However, despite numerous studies that have predicted that charge doping mainly contributes to the structural phase transition in the intercalation process, a mechanistic understanding of the phase transition at the atomic level has not been fully revealed. Furthermore, the coupled effects of strain and other intrinsic or extrinsic factors on the intercalation‐induced phase transition have not been quantitatively determined. Herein, the progress of the intercalation‐induced phase transition is briefly overviewed and the knowledge gaps in the current understanding of phase transition and intercalation in 2D TMDCs are highlighted. To fully gain the microscopic picture of the intercalation‐induced phase transition, in situ multimodal probes to monitor the real‐time structure−property relationship during intercalation are suggested. The proposed research directions further direct material scientists to efficiently engineer phase transition pathways in 2D materials to explore novel functional phases.