In correlated electronic states, observation of size-dependent nucleation and melting is rarely reported, likely due to the extremely small length scales necessary to observe such effects for electronic states. Here, using $1T\text{−}\mathrm{Ti}{\mathrm{Se}}_2$ nanoflakes as a prototypical two-dimensional charge density wave (CDW) system, we perform in situ cryogenic electron microscopy with temperature down to 20 K and observe size-dependent melting of CDWs. Specifically, we observe a melting point depression of CDW for $1T\text{−}\mathrm{Ti}{\mathrm{Se}}_2$ flakes with lateral sizes less than 100 nm. By fitting experimental data to a Ginzburg-Landau model, we estimate a zero-temperature correlation length of 10–50 nm, which matches the reported CDW domain size for $1T\text{−}\mathrm{Ti}{\mathrm{Se}}_2$. As the flake size approaches the correlation length, the divergence of the CDW correlation length near the transition is cut off by the finite flake size, limiting long-range order and thereby lowering the transition temperature. For very small flakes whose size is close to the correlation length, we also observe absence of long-range CDW, as predicted by the model.

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• Charge density waves
• Transition metal dichalcogenides
• High-resolution transmission electron microscopy