Researchers Find New State of Material at the Nanoscale

FAYETTEVILLE, Ark. – Researchers at the University of Arkansas and University of California-Los Angeles have discovered a new kind of quantum state of material at the nanoscale level that appears at low temperatures.

Research professor Sergey Prosandeev and professor Laurent Bellaiche of the University of Arkansas and A.R. Akbarzadeh of the University of California-Los Angeles report the state, called incipient ferrotoroidics, in Physical Review Letters.

The researchers asked what happens to nanoscale materials at low temperatures. Classical mechanics predict that atoms stop moving at low temperatures, but quantum mechanics predict that atoms continue to vibrate even at low temperatures. Such quantum mechanical vibrations are known to cause the disappearance of the spontaneous electric polarization in some bulk materials, and these materials are called incipient ferroelectrics. However, scientists don’t know what happens to nanoscale materials at low temperatures.

“What about the nanoscale ferroelectrics? Do they show quantum effects? Do they suppress polarization or promote new properties?” Prosandeev asked.

To answer these questions, the researchers modified the complicated computer codes aimed at resolving the behavior of bulk incipient ferroelectrics at low temperatures so they would describe nanostructures. They used the high-performance computing facility Star of Arkansas to perform the calculations. They performed both classical and quantum mechanics calculations, some of which took weeks using 128 processors.

At low temperatures, they discovered a new kind of quantum state of material. Called incipient ferrotoroidics, it is a state where quantum vibrations wash out the formation of recently discovered vortex states. This creates a situation where the material’s susceptibility to toroidal moment is high and independent of temperature – meaning that a small, curled field can create a strong vortex at any given moment.

“In electric capacitors we have electrons,” Prosandeev said. “Here we have topological charges instead.”

This means that it should be possible to create a new kind of device — namely, a topological charge capacitor — in nanoscale material at low temperatures. A vortex could be triggered in such a material using small changes in some chiral electric field.

“We predict that there is a way to prepare this original state of material,” Prosandeev said. “This opens the door to a new direction for applications and for thinking.”

This research was supported by grants from the Office of Naval Research and the National Science Foundation.