Electrically-tunable positioning of topological defects in liquid crystals

John J Sandford O’Neill,Stephen M Morris,Patrick S Salter,Steve J Elston,Martin J Booth

doi:10.1038/s41467-020-16059-1

John J Sandford O’Neill, Stephen M Morris + Show 3 more

Open Access

https://doi.org/10.1038/s41467-020-16059-1

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Journal: Nature Communications	Publication Date: May 5, 2020
Citations: 34	License type: open-access

Affiliation: University of Oxford

Abstract

Topological defects are a consequence of broken symmetry in ordered systems and are important for understanding a wide variety of phenomena in physics. In liquid crystals (LCs), defects exist as points of discontinuous order in the vector field that describes the average orientation of the molecules in space and are crucial for explaining the fundamental behaviour and properties of these mesophases. Recently, LC defects have also been explored from the perspective of technological applications including self-assembly of nanomaterials, optical-vortex generation and in tunable plasmonic metamaterials. Here, we demonstrate the fabrication and stabilisation of electrically-tunable defects in an LC device using two-photon polymerisation and explore the dynamic behaviour of defects when confined by polymer structures laser-written in topologically discontinuous states. We anticipate that our defect fabrication technique will enable the realisation of tunable, 3D, reconfigurable LC templates towards nanoparticle self-assembly, tunable metamaterials and next-generation spatial light modulators for light-shaping.

Highlights

Topological defects are a consequence of broken symmetry in ordered systems and are important for understanding a wide variety of phenomena in physics
In this study we use liquid crystals (LCs) pi-cell devices, which enable electricaladdressing of a layer of nematic LC aligned between parallelrubbed glass substrates[29]
Applying a voltage initially causes the alignment to distort, forming first an asymmetric homogeneous splay state (H-state) (“Hastate”) and, as the voltage is increased above a critical voltage, Vc, the bend state (“V-state”) (Supplementary Fig. 1a)

Summary

Introduction

Topological defects are a consequence of broken symmetry in ordered systems and are important for understanding a wide variety of phenomena in physics. In liquid crystals (LCs), defects exist as points of discontinuous order in the vector field that describes the average orientation of the molecules in space and are crucial for explaining the fundamental behaviour and properties of these mesophases. We demonstrate the fabrication and stabilisation of electrically-tunable defects in an LC device using two-photon polymerisation and explore the dynamic behaviour of defects when confined by polymer structures laser-written in topologically discontinuous states. It has been crucial to the development of understanding in the topology of materials that the mathematics used to describe the formation and evolution of topological defects can be transferred across different length-scales and between different disciplines To this end, defects in liquid crystals (LCs) have been investigated as highly-analogous laboratory systems for studying both superconductivity[2] and the evolution of the early-universe[5]. By translating the sample with respect to the focus of the laser, fine structures can be fabricated in 3D, with the possibility of achieving a resolution below the optical diffraction limit[25,26]

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