Kavli Affiliate: David A. Muller
| First 5 Authors: Saif Siddique, Saif Siddique, , ,
| Summary:
Classical nucleation theory predicts size-dependent nucleation and melting
due to surface and confinement effects at the nanoscale. 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-TiSe$_2$ nanoflakes
as a prototypical two-dimensional (2D) charge density wave (CDW) system, we
perform in-situ cryogenic electron microscopy with temperature down to 20 K and
observe size-dependent nucleation and melting of CDWs. Specifically, we observe
a melting point depression of CDW for 1T-TiSe$_2$ 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-TiSe$_2$. 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 CDWs, as
predicted by the model. We thus show that an electronic phase transition
follows classical nucleation theory.
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