As computing demands continue to surge, scientists are exploring the quantum world for smarter ways to process massive amounts of data. One promising direction is a field called orbitronics, which focuses on using the motion of electrons around an atom’s nucleus, known as orbital angular momentum, to carry and store information more efficiently. Traditionally, controlling this motion has required magnetic materials such as iron, which are heavy, costly, and difficult to scale for practical devices.
A new study has now introduced a far simpler approach to generating this orbital motion in electrons. The key lies in an emerging area of physics centered on chiral phonons.
Chiral Phonons Offer a Breakthrough
For the first time, researchers demonstrated that chiral phonons can directly transfer orbital angular momentum to electrons in a non-magnetic material. This finding removes a major limitation that has long held back orbitronics.
“The generation of orbital currents traditionally necessitates the injection of charge current into specific transition metals, and many of these elements are now classified as critical materials,” said Dali Sun, physicist at North Carolina State University and co-author of the study. “There are other ways to generate orbital angular momentum, but this method allows for the use of cheaper, more abundant materials.”
“We don’t need a magnet. We don’t need a battery. We don’t need to use voltage. We just need a material with chiral phonons,” added Valy Vardeny, distinguished professor in the Department of Physics & Astronomy at the University of Utah and co-author of the study. “Before, it was unimaginable. Now, we’ve invented a new field, so to speak.”
The research was led by North Carolina State University, with contributions from multiple institutions including the University of Utah, and was published on in the journal Nature Physics.
Understanding Chirality and Atomic Motion
The advance relies on how atoms are arranged and how they move inside materials. In solids, atoms form tightly packed lattice structures. In many materials such as metals, these structures are symmetrical, meaning their mirror image looks identical.
Chiral materials are different. In substances like quartz, atoms are arranged in a spiral pattern, similar to the threads of a screw. These structures have a built-in twist, either left- or right-handed, that cannot be superimposed on its mirror image. Human hands are a simple example of chirality.
Atoms in solids are not static. They vibrate in place. In symmetrical materials, this motion tends to be side-to-side. In chiral materials, the twisted structure causes atoms to move in a circular or spiral-like pattern.
How Chiral Phonons Move Energy
These vibrations can travel through a material as collective waves known as phonons. In chiral materials, these waves also follow a circular motion, forming chiral phonons. A helpful way to picture this is a crowd at a concert where one person starts swaying and the motion spreads through the group.
Because the atoms move in a circular path, they carry angular momentum. The researchers showed that this motion can be passed directly to electrons, giving them orbital angular momentum without relying on traditional magnetic methods.
Quartz Reveals Hidden Magnetic Effects
Electrons carry a negative charge, so magnetic fields are typically needed to influence their motion. Quartz, however, offers a surprising advantage. It is lightweight, inexpensive, and its chiral phonons generate their own internal magnetic effects.
For the first time, scientists at the University of Utah directly measured this magnetism in quartz using specialized equipment at the National High Magnetic Field Lab in Florida. By shining lasers through the material and studying how the reflected light changed in color, wavelength, etc., they confirmed that chiral phonons in quartz produce a significant magnetic field.
“Even though the material itself isn’t magnetic, the existence of chiral phonons gives us these magnetic levers to pull on,” said Rikard Bodin, doctoral candidate at the U and co-author of the paper. “When we talk about discovering things, like the orbital Seebeck effect — I can’t tell you that your TV is going to run on it, but it’s creating more levers that we can pull on to do new things. Now that it’s here, someone else can push it forward and before you know it, it’s ubiquitous. That’s how technology is.”
Aligning Phonons to Drive Electron Flow
Under normal conditions, chiral phonons exist in a mix of left- and right-handed states with varying energy levels. To test their concept, the researchers used α-quartz, a crystal with a naturally chiral structure. By applying a magnetic field, they were able to align these phonons.
Once enough phonons were aligned, their collective motion transferred to electrons, even after the external magnetic field was removed. This produced a flow of orbital angular momentum, which the team named the orbital Seebeck effect, drawing inspiration from the spin Seebeck effect that influences electron spin.
To detect this effect, the scientists layered metals (tungsten and titanium) on top of the α-quartz. This setup converted the otherwise hidden orbital motion into an electrical signal that could be measured.
Toward More Efficient Electronics
The approach is not limited to quartz. It can also be applied to other chiral materials such as tellurium, selenium, and hybrid organic/inorganic perovskites. Compared to existing methods, it requires fewer materials and allows the orbital motion to persist much longer.
This combination of simplicity, efficiency, and scalability could make orbitronics a more practical option for future technologies, potentially leading to faster and more energy-efficient devices.
The study involved a wide 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 Pennsylvania State University.
Source:
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