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Chiral Photons Convert Wasted Heat into Spin Information Without Magnetic Materials

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

Image Credit: agsandrew/

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

Spintronic devices are electronic devices that exploit the spin of an electron, instead of its charge, to make current utilized for data storage, communication, and computing.

Spin caloritronic devices have gained this name since they make use of thermal energy to make spin currents. Also, they are capable since 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.

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,” states Jun Liu, associate professor of mechanical and aerospace engineering at NC State and ORaCEL member.

Both Liu and Sun are co-corresponding authors of the study, appearing in the journal Nature Materials.

Chiral phonons are considered 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.

Dali Sun, Associate Professor and Member, Organic and Carbon Electronics Lab, North Carolina State University

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 stated, “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.

Dali Sun, Associate Professor and Member, Organic and Carbon Electronics Lab, North Carolina State University

The study was financially supported by the National Science Foundation and the US Department of Energy. Wei You, 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.

Journal Reference:

Kim, K., et al. (2023) Chiral-phonon-activated spin Seebeck effect. Nature Materials.

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