NC State University: 'We have successfully used chiral phonons to generate a spin current at room temperature without the need for magnetic materials'

Researchers from North Carolina State University and the University of North Carolina at Chapel Hill have made a groundbreaking discovery by using chiral phonons to convert wasted heat into spin information without the need for magnetic materials. 

This finding opens up possibilities for developing new classes of cost-effective and energy-efficient spintronic devices that can be utilized in various applications, including computational memory and power grids.

A significant advancement in the field of spintronics has been achieved by researchers from North Carolina State University and the University of North Carolina at Chapel Hill. 

They have successfully utilized chiral phonons to convert wasted heat into spin information, eliminating the need for magnetic materials. This breakthrough discovery has the potential to revolutionize spintronic device development, leading to cost-effective and highly energy-efficient devices suitable for computational memory and power grids. 

Unlike traditional electronic devices, spintronic devices utilize the spin of electrons instead of their charge to generate current for tasks such as data storage, communication, and computing. 

Spin caloritronic devices, a specific type of spintronics, show great promise by efficiently converting waste heat into spin information. However, current spin caloritronic devices rely on magnetic materials for creating and controlling electron spin.

Associate professor of physics and member of the Organic and Carbon Electronics Lab (ORaCEL) at North Carolina State University shared more about the study.

"We have successfully used chiral phonons to generate a spin current at room temperature without the need for magnetic materials," Dali Sun said.

Jun Liu, associate professor of mechanical and aerospace engineering at NC State and ORaCEL member, adds, 

"By applying a thermal gradient to a material containing chiral phonons, we can manipulate their angular momentum and create and control spin current."

Both Liu and Sun serve as co-corresponding authors of the research, which has been published in Nature Materials. Chiral phonons are groups of atoms that exhibit circular motion when stimulated by an energy source, such as heat. 

As these phonons propagate through a material, they transmit the circular motion, known as angular momentum, within it. This angular momentum serves as the source of spin, and the chirality of the phonons determines the direction of the spin. 

"Chiral materials are those that cannot be superimposed on their mirror image," Sun said. "Think of your right and left hands—they are chiral. You cannot wear a left-handed glove on your right hand or vice versa. This 'handedness' allows us to control the spin direction, which is crucial for using these devices in memory storage."

To demonstrate the generation of spin currents through chiral phonons, the researchers conducted experiments on a two-dimensional layered hybrid organic-inorganic perovskite. They introduced heat to the system by creating a thermal gradient. 

"A gradient is necessary because the temperature difference within the material, from hot to cold, drives the motion of the chiral phonons," Liu said. "The thermal gradient also enables us to utilize captured waste heat to generate spin current." 

The researchers anticipate that their work will lead to the development of spintronic devices that are more cost-effective and can be employed in a wider range of applications. 

"By eliminating the need for magnetism in these devices, we are expanding the possibilities in terms of the materials that can be used," Liu said. "This also translates to increased cost-effectiveness."

"Using waste heat instead of electric signals to generate spin current enhances the energy efficiency of the system, and the devices can operate at room temperature," Sun said. "This breakthrough could potentially unlock a much broader range of spintronic devices compared to what is currently available." 

The research received support from the National Science Foundation and the U.S. Department of Energy. Wei You, a professor of chemistry at the University of North Carolina at Chapel Hill and a member of ORaCEL, is also a co-corresponding author of the study.