Observation of two-step melting on a sphere

Area of Science:

• Condensed matter physics
• Materials science
• Statistical mechanics

Background:

• Melting in 2D flat space typically occurs in two steps via a hexatic phase.
• Melting on curved surfaces and the role of topological defects remain largely unknown.
• Crystalline particle assemblies on curved surfaces inherently possess defects, which can exhibit ordered structures.

Purpose of the Study:

• To investigate the melting process of colloidal crystals on a spherical surface.
• To probe the interplay between crystalline order and defect order during melting in situ.
• To determine if melting on a sphere follows similar pathways to flat surfaces.

Main Methods:

• Tuning interparticle interactions in situ to induce melting.
• Observing colloidal crystals on a spherical substrate.
• Analyzing crystalline order, defect order (specifically icosahedral ordering), and phase transitions.

Main Results:

• An intermediate hexatic phase was observed during the melting of colloidal crystals on a sphere.
• A significant drop in icosahedral defect order was noted in the hexatic phase.
• The melting process on the sphere exhibited characteristics of ideal melting, deviating from observations in flat space.

Conclusions:

• Melting on curved surfaces involves the loss of both crystalline and defect order.
• The hexatic phase plays a critical role in the melting dynamics on spheres.
• Findings impact understanding of viral capsid self-assembly and phase transitions in curved geometries.