New theory on liquid crystals with high symmetry (article in Physical Review X by LION PI Jan Zaanen et al.)


LCD screens use liquid crystals which have a high degree of order, even though they form a fluid. A new theory maps out the interplay between order, temperature and symmetry. Publication in Physical Review X.

Chances are that you’re staring at a collection of liquid crystals right now. Most screens nowadays are LCDs, meaning that they have a number of liquid crystals in every pixel. The computer determines for each pixel whether it blocks light or let it pass, by sending small currents through the liquid crystals. That way the correct color filters give the pixel the appropriate color.

LCD technology needs a certain amount of order. If the screen gets too hot, the liquid crystals will convert into a useless, chaotic, ordinary fluid. At room temperature they also form a fluid, but they have the necessary degree of orientation order. Leiden theoretical physicist Prof. Jan Zaanen and his group now formulated a theory on the interplay between symmetry, order and temperature.

The more symmetric a liquid crystal is, the colder it needs to be to still contain sufficient order. After all, it is harder to notice a crooked part in a composition with symmetry in many directions. In the figure below we see the ordered state on the left—displayed in purple in the graph. With low symmetry (left in graph) it abides even at high temperatures, but with high symmetry (right in graph) this takes extreme cold.

Ke Liu, Jaakko Nissinen, Robert-Jan Slager, Kai Wu, and Jan Zaanen, 'Generalized Liquid Crystals: Giant Fluctuations and the Vestigial Chiral Order of I, O, and T Matter', Physical Review X

The figure on the left displays the ordered state. In the graph this is represented in purple. With low symmetry (left in graph) the ordered state abides even at high temperatures, but with high symmetry (right in graph) this takes extreme cold.