Opening the door to more efficient orbitronic devices

Electrons have three intrinsic properties: spin, charge and orbital angular momentum. Researchers have long studied how to use spin to more efficiently create an electrical current. But the field of orbitronics—which is based upon using an electron's orbital angular momentum, rather than its spin, to create a current flow—remains relatively new.

"Traditionally, it has been technically challenging to generate orbital current," says Dali Sun, a professor of physics and member of the Organic and Carbon Electronics Lab (ORaCEL) at NC State University.

In a recent study, however, Sun and an international team of researchers demonstrated a groundbreaking new method to generate orbital current.

"There are other ways to generate orbital angular momentum, but this method allows for the use of cheaper, more abundant materials," says Sun, a co-author of the study, which was published in Nature Physics.

The research team's new method is the most efficient way yet to generate orbital angular momentum in electrons. And it's all thanks to a breakthrough discovery in one of the hottest topics in modern physics, a phenomenon known as chiral phonons.

Chiral phonons are groups of atoms that move in a circular direction when excited by an energy source such as heat. As the phonons move through a material, they propagate that circular motion—or angular momentum—through it.

"In this work, we show that we can use that angular momentum from the chiral phonon and convert it to orbital current instead of spin," says Jun Liu, a co-corresponding author of the study, who's an associate professor of mechanical and aerospace engineering at NC State and a member of ORaCEL.

The researchers showed for the first time ever that chiral phonons can directly transfer orbital angular momentum to electrons in a non-magnetic material.

"We don't need a magnet. We don't need a battery. We don't need to use voltage. We just need a material with chiral phonons," study co-author Valy Vardeny, a distinguished professor in the University of Utah's Department of Physics & Astronomy, said. "Before, it was unimaginable. Now, we've invented a new field, so to speak."

The researchers hope their work will help open the door to more cost-effective orbitronic applications.

"The work also answers fundamental questions around the interplay between structural chirality and orbital currents, which will hopefully help expand the field of orbitronics further," Sun says.

Provided by North Carolina State University