With the research group of Dong Ki Yoon at KAIST (Korea), we explain how topological defect configurations in the nematic liquid crystal (LC) phase can be “remembered” in the smectic LC phase after a phase transition. This geometric memory allows near-perfect recovery of the original defects upon reversing the phase transition, and can be controllably erased to generate a new defect pattern.
The preprint is available at https://arxiv.org/abs/1904.05507.
A thin, hybrid-aligned film of the liquid crystal 8CB is cooled from the nematic phase to the smectic-A phase, replacing the nematic boojum configuration (fourfold dark brush crossings) with a packing of smectic focal conic domains. Melting the smectic-A phase back into the nematic phase recovers most details of the original boojum configuration.
Numerical modeling shows that toric focal conic domain packings melt into arrays of three types of boojums upon heating from the smectic-A phase to the nematic phase, helping to explain the experimentally observed creation of large numbers of boojums.