Orbitronics: A new path to more efficient technologies

An international team of scientists, including Maia Vergniory, Professor in the Department of Physics and member of the Quantum Institute from Sherbrooke University, has confirmed the existence of orbital monopoles in topological chiral crystals. This discovery, published in Nature Physics, opens up promising prospects for exploiting the orbital angular momentum of electrons, a phenomenon at the heart of an emerging field of quantum physics: orbitronics.

The growth of modern technologies is accompanied by massive and constantly increasing energy consumption. As we seek to miniaturize and maximize the power of our devices, a crucial question arises: how can we improve their energy efficiency? One innovative answer could lie in orbitronics.

From Electronics to Orbitronics

For decades, electronics have relied on the charge of the electron to process and store information. However, quantum physics offers us other avenues: among them, the use of the electron’s spin – the classical equivalent of the electron’s rotation on itself – has given rise to spintronics. Another possibility emerges with orbital angular momentum – the equivalent of the electron’s rotation around the nucleus – which provides us with a third option: orbitronics.

Orbital angular momentum offers unique advantages: it enables information to be transmitted with minimal energy loss, thus reducing thermal dissipation – a major challenge for current technologies. However, exploiting this property in concrete devices requires a specific type of material capable of preserving and controlling these orbital states. The search for such materials has led researchers to explore topological chiral crystals.

Crystals With Unique Properties

Topological chiral crystals combine their chirality – an asymmetry comparable to that between right and left hands – and their topology – the study of properties that remain invariant even when an object is deformed – to create robust and unique electronic states. These crystals feature a unique spiral structure, ideal for manipulating the orbital angular momentum of electrons. Another special feature of topological chiral crystals is that they exhibit a theoretical state known as orbital monopole, in which the orbital angular momentum of the electrons is perfectly symmetrical in all directions. This property could revolutionize information transmission by making communication possible in all directions. Until now, this monopole existed only in theoretical predictions.

This is where the work of Professor Vergniory and her colleagues come in. Their aim: to move from theory to experimental proof.

Finding the Monopole

The researchers studied two topological chiral crystals: PtGa and PdGa. Using angle-resolved photoelectron spectroscopy (ARPES), and incorporating circular polarization of the light, they studied the interaction of photons with the electrons in these crystals. By carefully modifying the photons’ energy, they observed a remarkable phenomenon: the measured signal appeared to “rotate” around the orbital monopoles, confirming their existence.

The team not only visualized the orbital angular momentum monopoles, but also showed that their polarity could be reversed using a crystal of opposite chirality. This discovery is crucial for developing orbitronic devices capable of transmitting information in specific directions.

This work unifies theory and experiment, opening up prospects for further exploration of the unique properties of these materials. This methodological breakthrough also provides the scientific community with new tools and could inspire future discoveries, enriching our understanding of quantum materials and their possible applications.