Creation of topological charges by the spontaneous symmetry breaking phase transition in azo dye-doped nematic liquid crystals

Abstract

Liquid crystals are anisotropic fluids with long-range directional order. They can be easily used to create topological defects, but creating a controlled topological defect is difficult and involves many tasks and complex processes. However, in our study, we were able to easily generate disclinations in the symmetry-breaking boundaries of an azo dye-doped nematic liquid crystal cell owing to photoisomerization and symmetry-breaking isotropic-nematic phase transition. The method proposed here marks the starting point for the easier control of topological defects in liquid crystals.

Generation of the Planar Solitons Using Thermal Trapping of a Disclination in Nematic Liquid Crystals and Their Applications

“…To generate solitons, we first created a k = ±1/2 disclination pair (topological dipole) in a uniform nematic as shown in Figure a–d, by using the thermal and photoisomerization effects. [ 10 ] The created topological charge pairs are shown in Figure 2a through the images of polarizing optical microscopy (POM) with a half‐wave plate (HWP). The colors shown in the image of POM with HWP (POMH) provide information of the orientation of the NLC molecules.…”

“…The cutting of soliton is due to the I–N phase transition and not due to the photoalignment effect by photoisomerization, so it does not matter which polarization of the laser light is used. However, if the polarization of laser light in a direction parallel to the alignment direction of LCs is used, the absorption of dye aligned parallel to the LCs increases at the beginning, [ 10 ] giving a greater thermal effect, so less laser power can be used.…”

“…This is because in cells using epoxy‐coated substrates, the transport speed was measured to be small due to friction between substrates and the bead or dye adsorption. [ 10 ]…”

“…[ 1,2 ] A topological defect is created when symmetry breaking occurs and can be created easily in NLCs by breaking symmetry in ways such as dispersion of topological colloids, [ 3–5 ] incidence of laser light, [ 6,7 ] modulation of boundary conditions, [ 8,9 ] and isotropic–nematic (I–N) phase transitions. [ 10–12 ]…”

“…[1,2] A topological defect is created when symmetry breaking occurs and can be created easily in NLCs by breaking symmetry in ways such as dispersion of topological colloids, [3][4][5] incidence of laser light, [6,7] modulation of boundary conditions, [8,9] and isotropicnematic (I-N) phase transitions. [10][11][12] Topological defects lacking singularity are called topological solitons, which include planar solitons, [13][14][15] linear solitons, [1] and particle-like solitons. [1,16,17] A π-wall with a constant thickness and a termination in k = ±1/2 disclinations (line defects) is called the planar soliton, which is the result of symmetry breaking when a k = +1/2 or −1/2 disclination is moved.…”