Scientists discover breakthrough materials to enhance light-based computers

New York University

Researchers have been developing computers that deploy light, or photons, rather than electricity to power storage and calculations. These light-based computers have the potential to be more energy efficient than traditional computers while also running calculations at greater speeds.

However, a major challenge in the production of light-based computers—still in their infancy—is successfully rerouting microscopic light signals on a computer chip with minimal loss in signal strength. This is fundamentally a materials-design problem. These computers require a lightweight material to block additional light from all incoming directions—what’s known as an “isotropic bandgap material”—in order to maintain signal strength.

Scientists at New York University report the discovery of “gyromorphs”—a material that combines the seemingly incompatible properties of liquids and crystals and that performs better than any other known structure in blocking light from all incoming angles. The breakthrough, described in the journal Physical Review Letters, marks an innovative way to control optical properties and to potentially advance the capabilities of light-based computers.

“Gyromorphs are unlike any known structure in that their unique makeup gives rise to better isotropic bandgap materials than is possible with current approaches,” says Stefano Martiniani, an assistant professor of physics, chemistry, mathematics and neural science, and the paper’s senior author.

In designing isotropic bandgap materials, scientists have frequently turned to quasicrystals—first conceived by physicists Paul Steinhardt and Dov Levine in the 1980s and simultaneously observed in experiments by Dan Schechtman, who received the Nobel Prize in Chemistry in 2011. Quasicrystals have a mathematical order to their structure, but, unlike a crystal, one that does not repeat.

However, there is an unfortunate trade-off in quasicrystals, the NYU researchers note: either they block out light completely, but only from a few directions, or they attenuate light from all directions, but do not quite block it. That is why scientists have continued to seek alternative materials that can block out signal-sapping light.

In the Physical Review Letters work, the NYU researchers created “metamaterials,” which are engineered materials with properties stemming from their structure rather than their chemical nature. However, a challenge in creating metamaterials is first understanding how their structure gives rise to physical properties of interest.

To address these challenges, the scientists developed an algorithm to design disordered structures that were functional. In doing so, they discovered a novel form of “correlated disorder”—materials that are neither fully disordered nor fully ordered.

“Think of trees in a forest—they grow at random positions, but not completely random because they’re usually a certain distance from one another,” explains Martiniani. “This new pattern, gyromorphs, combines properties that we believed to be incompatible and displays a function that outperforms all ordered alternatives, including quasicrystals.”

The researchers noticed that every single isotropic bandgap material had a structural signature in common.

“We wanted to make this structural signature as pronounced as possible,” adds Mathias Casiulis, a postdoctoral fellow in NYU’s Department of Physics and the paper’s lead author. “The result was a new class of materials—gyromorphs—that reconcile seemingly incompatible features.

“This is because gyromorphs don’t have a fixed, repeating structure like a crystal, which gives them a liquid-like disorder, but, at the same time, if you look at them from a distance they form regular patterns. These properties work together to create bandgaps that lightwaves can’t penetrate from any direction.”