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[PNAS] Cross-talk between topological defects in different fields revealed by nematic microfluidics


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 cross-talk 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 star-shaped 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

Luca Giomia, Žiga Kosb, Miha Ravnikb,c, and Anupam Senguptad,e,1,2 Author Affiliations

aInstituut-Lorentz for Theoretical Physics, Leiden University, 2333 CA Leiden, The Netherlands; bFaculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia; cCondensed Matter Physics Department, Jožef Stefan Institute, 1000 Ljubljana, Slovenia; dInstitute for Environmental Engineering, Department of Civil, Environmental, and Geomatic Engineering, Eidgenössische Technische Hochschule (ETH) Zurich, 8093 Zurich, Switzerland; eMax-Planck-Institute for Dynamics and Self-Organization, 37077 Goettingen, Germany Edited by Tom C. Lubensky, University of Pennsylvania, Philadelphia, PA, and approved June 1, 2017 (received for review February 17, 2017)

Link: http://www.pnas.org/content/early/2017/06/30/1702777114

#07072017 #MaterialScience

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