Chiral Phonons: The Key to Energy-Efficient Orbital Currents in Magnetic Devices

Electrons’ orbital angular momentum could help create energy-efficient, low-power magnetic devices. These orbital currents usually come from 3d transition-metal magnets. They are generated either by an applied electric field or by changes in magnetization. Chiral phonons are vibrations where atoms move in a circular pattern when energized, for example, by heat. As these vibrations travel through a material, they carry and spread that circular motion, known as angular momentum, along with them. A new study shows that chiral phonons can generate orbital currents without the use of magnetic materials. This works because chiral phonons carry their own magnetic moments. The effect is known as the orbital Seebeck effect. This effect can also occur in everyday crystal materials. The discovery could lead to cheaper, energy‑efficient orbitronic devices for many types of electronics. Twist-angle engineering unlocks phonon control for next-gen quantum materials The researchers observed orbital currents mostly in tungsten and titanium films on quartz, using the inverse orbital Hall effect. Dali Sun, co-corresponding author on the study, said, “This work shows that we can use a heat gradient to drive out chiral phonons in a quartz (i.e., SiO2) substrate, and the chiral phonons can be converted into orbital current.” “There are other ways to generate orbital angular momentum, but this method allows for the use of cheaper, more abundant material.” Earlier research showed that spin currents can be generated in non‑magnetic hybrid semiconductors with chiral phonons by applying a thermal gradient. The new study demonstrates that the angular momentum of chiral phonons can instead be converted into orbital currents. Jun Liu, associate professor of mechanical and aerospace engineering at NC State and member of ORaCEL, stated, “And we can do it in very simple non-magnetic insulators containing chiral phonons, because the rotation of the chiral phonon generates magnetism.” Authors noted, “Our findings hold promise for orbitronics based on chiral phonons in non-magnetic insulators and shed light on the fundamental understanding of chiral phonons and their interaction with electron orbitals.” Journal Reference: