Coupled Sublattice Melting and Charge-Order Transition in Two Dimensions

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Two-dimensional (2D) melting is a complex phase transition.
• Theoretical models predict a two-step melting via topological defect unbinding.
• Understanding 2D melting mechanisms is crucial for novel material applications.

Purpose of the Study:

• Investigate the melting transition of a charge-ordered K-Sn alloy monolayer on a silicon substrate.
• Elucidate the atomistic processes and distinct stages of the melting transition.
• Provide experimental and theoretical insights into 2D materials' phase behavior.

Main Methods:

• Combined experimental and theoretical analysis.
• Observation of K sublattice positional fluctuations and diffusion.
• Characterization of Sn host lattice charge order collapse.

Main Results:

• A novel, multistep melting transition was observed in the 2D K-Sn alloy.
• Melting initiated with short-range K sublattice fluctuations, followed by domain diffusion.
• The Sn host lattice charge order exhibited a multistep collapse with displacive and order-disorder characteristics.

Conclusions:

• The study presents a rare, detailed view of a multistep melting transition in a 2D system.
• Findings challenge and refine existing theoretical models of 2D phase transitions.
• This work advances the understanding of phase transitions in low-dimensional materials.