Crosstalk between topological defects in different fields revealed by nematic microfluidics
Abstract
Topological defects are singularities in material fields that play a vital role across a range of systems: from cosmic microwave background polarization to superconductors and biological materials. Although topological defects and their mutual interactions have been extensively studied, little is known about the interplay between defects in different fields—especially when they coevolve—within the same physical system. Here, using nematic microfluidics, we study the crosstalk of topological defects in two different material fields—the velocity field and the molecular orientational field. Specifically, we generate hydrodynamic stagnation points of different topological charges at the center of starshaped microfluidic junctions, which then interact with emergent topological defects in the orientational field of the nematic director. We combine experiments and analytical and numerical calculations to show that a hydrodynamic singularity of a given topological charge can nucleate a nematic defect of equal topological charge and corroborate this by creating <mml:math><mml:mrow><mml:mo></mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math>1, <mml:math><mml:mrow><mml:mo></mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>2, and <mml:math><mml:mrow><mml:mo></mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:math>3 topological defects in four, six, and eightarm junctions. Our work is an attempt toward understanding materials that are governed by distinctly multifield topology, where disparate topologycarrying fields are coupled and concertedly determine the material properties and response.
 Publication:

Proceedings of the National Academy of Science
 Pub Date:
 July 2017
 DOI:
 10.1073/pnas.1702777114
 arXiv:
 arXiv:1612.00095
 Bibcode:
 2017PNAS..114E5771G
 Keywords:

 multifield topology;
 nematic liquid crystals;
 topological defects;
 microfluidics;
 crossinteractions;
 Condensed Matter  Soft Condensed Matter
 EPrint:
 18 pages, 9 figures