As the demand for computing continues to soar, scientists are exploring the quantum world for smarter ways to process large amounts of data. One promising direction is a field called orbitronics, which focuses on harnessing the movement of electrons around the nucleus, known as orbital angular momentum, to more efficiently transport and store information. Traditionally, controlling this movement required magnetic materials such as iron, which were heavy, expensive, and difficult to scale to fit into actual devices.
New research introduces a much simpler approach to producing this orbital motion in electrons. The key lies in a new area of physics centered on chiral phonons.
Chiral phonons bring breakthrough
Researchers have demonstrated for the first time that chiral phonons can directly transfer orbital angular momentum to electrons in non-magnetic materials. This discovery removes a major limitation that has long held back orbitronics.
“Generation of orbital current traditionally requires injection of charging current into certain transition metals, and many of these elements are now classified as critical materials,” said Dali Sun, a physicist at North Carolina State University and co-author of the study. “There are other ways to generate orbital angular momentum, but this method uses cheaper and more abundant materials.”
“You don’t need a magnet. You don’t need a battery. You don’t need to use a voltage. You just need a material with chiral phonons,” added Vallie Vardeny, distinguished professor in the University of Utah’s Department of Physics and Astronomy and co-author of the study. “It was unimaginable before. Now we have, so to speak, invented a new field.”
The study, led by North Carolina State University with contributions from multiple institutions including the University of Utah, was published in the journal Science. natural physics.
Understanding chirality and atomic motion
This progress depends on how atoms are arranged and how they move within matter. In solids, atoms form a tightly packed lattice structure. In many materials, such as metals, these structures are symmetrical and mirror images appear identical.
Chiral substances are different. In materials like quartz, the atoms are arranged in a spiral pattern, like the threads of a screw. These structures incorporate left-handed or right-handed twists that cannot be superimposed on mirror images. The human hand is a simple example of chirality.
Atoms in solids are not static. It vibrates on the spot. For symmetrical materials, this movement tends to occur from side to side. In chiral materials, the twisted structure causes the atoms to move in a circular or helical pattern.
How chiral phonons transfer energy
These vibrations travel through matter as collective waves known as phonons. In chiral materials, these waves also follow circular motion, forming chiral phonons. An easy way to imagine this is when there’s a crowd at a concert, one person starts swaying, and the movement spreads throughout the group.
Because atoms move in circular orbits, angular momentum is transferred. The researchers showed that this motion is transmitted directly to the electrons, giving them orbital angular momentum without relying on traditional magnetic methods.
Quartz reveals hidden magnetic effects
Because electrons have a negative charge, a magnetic field is usually required to affect their movement. However, quartz has surprising benefits. It is lightweight and cheap, and its chiral phonons generate a unique internal magnetic effect.
Scientists at the University of Utah have directly measured this magnetism in quartz for the first time using specialized equipment at the National High Magnetic Field Laboratory in Florida. By irradiating the material with a laser and studying how the color and wavelength of the reflected light change, they confirmed that chiral phonons in quartz generate a large magnetic field.
“Although the material itself is not magnetic, the presence of chiral phonons allows us to pull the magnetic lever,” said Ricardo Bourdain, an American doctoral candidate and co-author of the paper. “When we talk about discoveries, like the orbital Seebeck effect, we can’t say that television will run on it, but there are more levers that we can pull to do new things. Now that it’s here, someone else can move it forward, and before we know it, it becomes ubiquitous. That’s how technology works.”
Aligning phonons to drive electron flow
Under normal conditions, chiral phonons exist in a mixture of left-handed and right-handed states with different energy levels. To test their concept, the researchers used alpha-quartz, a naturally chiral crystal. By applying a magnetic field, they were able to align these phonons.
When enough phonons are aligned, their collective motion is transferred to the electron even after the external magnetic field is removed. This creates a flow of orbital angular momentum, which the researchers named the orbital Seebeck effect, inspired by the spin Seebeck effect that affects the spin of electrons.
To detect this effect, scientists layered metals (tungsten and titanium) on top of alpha quartz. This setup converted the hidden orbital motion into a measurable electrical signal.
Aiming for more efficient electronics
This approach is not limited to quartz. It can also be applied to other chiral materials such as tellurium, selenium, and organic/inorganic hybrid perovskites. Compared to existing methods, it requires less material and allows orbital motion to last longer.
This combination of simplicity, efficiency, and scalability makes orbitronics a more practical option for future technologies, potentially leading to faster and more energy-efficient devices.
The study involved a broad collaboration of researchers from institutions including North Carolina State University, the University of Utah, Nanjing Normal University, the Air Force Research Laboratory, the University of Washington, the University of North Carolina at Chapel Hill, the National High Magnetic Field Laboratory, the University of Illinois at Urbana-Champaign, the University of South Carolina, and the Pennsylvania State University.
