Nematic liquid crystals have been a hot topic in materials research since the 1970s. These materials exhibit a curious mix of fluid- and solid-like behaviors, which allow them to control light. Engineers have used them extensively to make the liquid crystal displays (LCDs) in many laptops, TVs and cellphones.

Think of nematic liquid crystals like dropping a handful of pins on a table. The pins in this case are rod-shaped molecules that are “polar”—with heads (the blunt ends) that carry a positive charge and tails (the pointy ends) that are negatively charged. In a traditional nematic liquid crystal, half of the pins point left and the other half point right, with the direction chosen at random.

A ferroelectric nematic liquid crystal phase, however, is much more disciplined. In such a liquid crystal, patches or “domains” form in the sample in which the molecules all point in the same direction, either right or left. In physics parlance, these materials have polar ordering.

Noel Clark, a professor of physics and director of the SMRC, said that his team’s discovery of one such liquid crystal could open up a wealth of technological innovations—from new types of display screens to reimagined computer memory.

“There are 40,000 research papers on nematics, and in almost any one of them you see interesting new possibilities if the nematic had been ferroelectric,” Clark said.

Under the microscope

The discovery is years in the making.

Nobel Laureates Peter Debye and Max Born first suggested in the 1910s that, if you designed a liquid crystal correctly, its molecules could spontaneously fall into a polar ordered state. Not long after that, researchers began to discover solid crystals that did something similar: Their molecules pointed in uniform directions. They could also be reversed, flipping from right to left or vice versa under an applied electric field. These solid crystals were called “ferroelectrics” because of their similarities to magnets. (Ferrum is Latin for “iron”).

In the decades since, however, scientists struggled to find a liquid crystal phase that behaved in the same way. That is, until Clark and his colleagues began examining RM734, an organic molecule created by a group of British scientists several years ago.

That same British group, plus a second team of Slovenian scientists, reported that RM734 exhibited a conventional nematic liquid crystal phase at higher temperatures. At lower temperatures, another unusual phase appeared.

When Clark’s team tried to observe that strange phase under the microscope they noticed something new. Under a weak electric field, a palette of striking colors developed toward the edges of the cell containing the liquid crystal.

“It was like connecting a light bulb to voltage to test it, but finding the socket and hookup wires glowing much more brightly instead,” Clark said.

Stunning results

So, what was happening?

The researchers ran more tests and discovered that this phase of RM734 was 100 to 1,000 times more responsive to electric fields than the usual nematic liquid crystals. This suggested that the molecules that make up the liquid crystal demonstrated strong polar order.