Year: 2025
Type: preprint
Abstract: The Lebwohl-Lasher model of uniaxial liquid crystals with (\textit{n} = 3, \textit{d} = 2) was reported earlier to undergo a crossover transition to a novel nematic phase at a temperature $T=T_{n}$. This phase has unbound topological defects in a nematic background, that pair at a lower $T_{\text{BKT}} < T_{n}$. The transition has zero latent heat, and a specific heat and correlation length that remain finite. We discover here a significant sparseness of states or an entropy barrier `bottleneck', between the isotropic and novel nematic phases. Passage through these sparse configurations is enabled by short-range nematic clusters dressing the defect cores. The free energy temperature derivatives, along with energy derivatives of the micro-canonical entropy, determine that this is a {\it third-order} transition in the Ehrenfest classification. The local transformation to dressed defects induces a sharp downward cusp in the correlation length, at a precursor temperature $T_{p} > T_{n}$. The entropic bottleneck manifests as a rippling of the free energy landscape, over mutually modifying nematic order and defect density. Cooling through $T_{p}$ yields an itinerant para-nematic fluid of dressed defects with macroscopically occupied local polar angle tilts, that catalyse a common global tilt or nematic phase at $T_{n}$.
Source: arXiv (Cornell University)
Authors: Latha, B. Kamala, Sastry, V. S. S., Shenoy, S. R.
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6948462865
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