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The orbital angular momentum of electrons has long been considered a minor physical phenomenon, suppressed in most crystals and largely overlooked. Scientists at Forschungszentrum Jülich have now discovered that in certain materials it is not only preserved but can even be actively controlled. This is due to a property of the crystal structure called chirality, which also influences many other processes in nature.

The discovery has the potential to lead to a new class of electronic components capable of transmitting information with exceptional robustness and energy efficiency.

From electronics to spintronics, and now to orbitronics: In classical electronics, it is primarily the charge of the electron that counts. In modern approaches such as quantum computing and spintronics, the focus has shifted to the electron's spin.

Now, another property is entering the spotlight: orbital angular momentum (OAM). In simple terms, OAM describes how the electron moves within an atom—not in a classical orbit, but as a quantum mechanical distribution within an orbital.

"For decades, spin was considered the key parameter for new quantum-based technologies. But orbital angular momentum also has great potential as an information carrier—and is significantly more robust," explains Dr. Christian Tusche from the Peter Grünberg Institute (PGI-6) at Forschungszentrum Jülich. The physicist is one of the lead authors of the study in Advanced Materials.

The orbital angular momentum is one of the fundamental quantum numbers of the electron, similar to spin, which describes the apparent rotation of the electron. However, OAM is rarely observable in crystals. It is usually suppressed by the symmetrical electric and magnetic fields in the crystal lattice—an effect known as "quenching."

In so-called chiral materials such as the cobalt silicide (CoSi) studied, this is different, as the team led by Dr. Tusche, together with partners in Taiwan, Japan, Italy, the U.S., and Germany, has now been able to show. The word "chiral" comes from the ancient Greek "cheir" for hand.

"These crystal structures lack mirror symmetry and are either left- or right-handed—just like the human hand. You can turn them around and they remain mirror images of each other," explains Dr. Tusche. Chirality occurs frequently in nature. Sugar molecules, amino acids, and DNA all exhibit chiral structures.

Using high-resolution momentum microscopy and circularly polarized light, the researchers were able to resolve the orbital angular momentum in the chiral semiconductor for the first time—both inside the crystal and on its surface.

For the measurements, they used the NanoESCA momentum microscope operated by Forschungszentrum Jülich at the Elettra synchrotron in Trieste, Italy. They discovered that the handedness of the crystal—left- or right-handed—predictably affects the orbital angular momentum of the electrons.

New link between crystal structure and electron

"Our results show that the structure of the crystal directly influences the angular momentum of the electrons—an effect that we were able to measure directly. This opens up a whole new door for materials research and information processing," emphasizes experimental physicist Dr. Ying-Jiun Chen.

Dr. Dongwook Go, theoretical physicist at the Peter Grünberg Institute (PGI-1) in Jülich, adds, "The discovery is particularly important for the emerging field of orbitronics, which uses orbital angular momentum as an information carrier for the next generation of quantum technology."

A characteristic feature of the resulting orbital angular momentum texture are differently formed Fermi arcs: open, arc-shaped structures that become visible in so-called momentum space representations, as generated by momentum microscopy.

This opens up new perspectives for applications. In the future, information could be transmitted and stored not just via the charge or spin of electrons, but also through the direction and orientation of their orbital angular momentum. This so-called orbitronics—electronics based on orbital properties—could thus provide the foundation for a new class of electronic devices.

Applications

The development of this future technology is part of the EIC Pathfinder project OBELIX, in which Prof. Yuriy Mokrousov from the University of Mainz is also involved. The theoretical physicist is also group leader at the Peter Grünberg Institute (PGI-1) in Jülich and contributed fundamental theoretical models to the recent discovery.

Prof. Claus Michael Schneider also sees great promise. "For instance, it seems conceivable to use orbital angular momentum as an information carrier. Or one might employ circularly polarized light to selectively influence a crystal's chirality, enabling a light-controlled, non-mechanical switch as an alternative to the transistor.

"Furthermore, coupling between orbital angular momentum and spin could allow integration into existing spintronics concepts—for example, in hybrid quantum devices," says the director of the Peter Grünberg Institute for Electronic Properties (PGI-6) at Forschungszentrum Jülich.