Researchers use chiral phonons to transform wasted heat into spin information without magnetic materials

Scientists at the North Carolina State University, the University of North Carolina at Chapel Hill and Nanjing Normal University have made use of chiral phonons to transform wasted heat into spin information—without requiring magnetic materials.

This achievement could result in new classes of affordable and energy-efficient spintronic devices for use in applications from computational memory to power grids.

Spin caloritronic devices have gained this name as they use thermal energy to make spin currents. Also, they have the potential to transform waste heat into spin information, which makes them highly energy efficient. But current spin caloritronic devices should consist of magnetic materials to make and control the spin of the electron.

"We used chiral phonons to create a spin current at room temperature without needing magnetic materials", said Dali Sun, Associate Professor and Member, Organic and Carbon Electronics Lab, North Carolina State University.

“By applying a thermal gradient to a material that contains chiral phonons, you can direct their angular momentum and create and control spin current,” explained Jun Liu, associate professor of mechanical and aerospace engineering at NC State and ORaCEL member.

Chiral phonons are groups of atoms that tend to move in a circular direction while being subjected to excitation by an energy source—in this case, heat. Since the phonons tend to move via a material, they distribute that circular motion, or angular momentum, through it. The angular momentum acts as the source of spin, and the direction of the spin is dictated by the chirality.

"Chiral materials are materials that cannot be superimposed on their mirror image. Think of your right and left hands—they are chiral. You can’t put a left-handed glove on a right hand, or vice versa. This ‘handedness’ is what allows us to control the spin direction, which is important if you want to use these devices for memory storage", said Sun.

By utilizing a thermal gradient to initiate heat to the system, the scientists illustrated chiral phonon-generated spin currents in a two-dimensional layered hybrid organic-inorganic perovskite.

Liu stated, “A gradient is needed because temperature difference in the material—from hot to cold—drives the motion of the chiral phonons through it. The thermal gradient also allows us to use captured waste heat to generate spin current.”

The scientists believe that the work will result in spintronic devices that are affordable to produce and could be utilized in an extensive range of applications.

Liu stressed: “Eliminating the need for magnetism in these devices means you’re opening the door wide in terms of access to potential materials. And that also means increased cost-effectiveness.”

"Using waste heat rather than electric signals to generate spin current makes the system energy efficient—and the devices can operate at room temperature. This could lead to a much wider variety of spintronic devices than we currently have available", said Sun.

Posted: Feb 17,2023 by Roni Peleg