Fingered core structure of nematic boojums

Area of Science:

• Soft Matter Physics
• Liquid Crystal Science
• Materials Science

Background:

• Boojums are topological defects found on surfaces of liquid crystal phases.
• Understanding their core structure is crucial for predicting material behavior.
• The Landau-de Gennes approach provides a framework for studying liquid crystal phase transitions and defect structures.

Purpose of the Study:

• To investigate the fine biaxial core structure of a boojum on a nematic liquid crystal surface.
• To analyze the influence of surface anchoring strength on the boojum's core structure and behavior.
• To elucidate the topological and physical mechanisms governing boojum expulsion.

Main Methods:

• Phenomenological modeling using the Landau-de Gennes approach.
• Analysis of the biaxial core structure, including finger and shell components.
• Investigation of defect behavior as a function of surface anchoring strength.

Main Results:

• The boojum core consists of a negatively uniaxial finger surrounded by a maximally biaxial shell.
• The dimensions of the finger and shell are comparable to the biaxial correlation length.
• The finger tip is topologically melted.
• Below a critical surface anchoring strength, the finger detaches from the bulk and is expelled from the surface.

Conclusions:

• The study reveals the detailed structure of a boojum core in nematic liquid crystals.
• Surface anchoring strength critically influences boojum stability and expulsion dynamics.
• The findings provide insights into topological defect behavior in soft matter systems.