Scientists have just taken a significant step toward a long-awaited dream by creating ultra-thin, magnetically-controlled quantum devices that don’t need bulky magnets to function.
In a groundbreaking study, a research team led by physicists at Delft University of Technology in the Netherlands has experimentally confirmed the elusive quantum spin Hall effect (QSH) in magnetic graphene, eliminating the need for an external magnetic field. This study represents a significant advancement in our understanding of quantum physics, opening up new possibilities for future technologies.
This first-of-its-kind achievement means future quantum circuitry could be smaller, faster, and far more practical than ever imagined.
“Spin is a quantum mechanical property of electrons, which is like a tiny magnet carried by the electrons, pointing up or down,” lead author and researcher at TU Delft and Harvard University, Dr. Talieh S. Ghiasi, explained in a statement. “We can leverage the spin of electrons to transfer and process information in so-called spintronics devices.”
“Such circuits hold promise for next-generation technologies, including faster and more energy-efficient electronics, quantum computing, and advanced memory devices.” This breakthrough not only validates theoretical predictions but also propels us into a future of advanced and efficient technologies.
The findings, published in Nature Communications, detail how the team successfully induced a quantum spin Hall state in graphene by layering it on top of a van der Waals antiferromagnetic material called CrPS₄.
This layered structure fundamentally alters the band structure of graphene, introducing spin-orbit and exchange interactions that are strong enough to give rise to exotic, topologically protected edge states. These special states allow electrons to move along the edges of the material without resistance and with their spins locked in opposite directions—a hallmark of QSH behavior.
For years, scientists have sought to harness spin—an intrinsic property of electrons—in place of charge to create next-generation “spintronic” devices. However, achieving long-distance, coherent spin transport —a state in which the spins of electrons remain in a fixed relationship over a long distance —has been notoriously difficult. Conventional methods required strong magnetic fields to split electron spins and create the necessary quantum edge states.
This study demonstrates that magnetism can originate from within. By carefully choosing a magnetic partner material for graphene—specifically, CrPS₄—the researchers induced both magnetism and spin-orbit coupling within the graphene itself. As a result, they achieved spin-polarized, helical edge states that persisted even at room temperature.
“The detection of the QSH states at zero external magnetic fields, together with the AH [anomalous Hall] signal that persists up to room temperature, opens the route for practical applications of magnetic graphene in quantum spintronic circuitries,” the researchers wrote in the study. This breakthrough paves the way for a new era of practical and efficient quantum technologies.
The experimental setup involved layering monolayer graphene on a flake of CrPS₄ and encapsulating it with hexagonal boron nitride (hBN). CrPS₄ is an air-stable magnetic semiconductor with a Néel temperature of around 38 K and strong interlayer antiferromagnetic coupling.
Using advanced electrical transport measurements, the team demonstrated that this configuration induces staggered potential and spin-orbit interactions within the graphene. These alterations open a topological gap in the graphene’s bulk, allowing gapless “helical” edge states to form—essentially creating a quantum spin Hall insulator.
Key evidence was obtained by measuring the conductance of the device near the charge neutrality point at zero magnetic fields. The conductance plateaued at precisely 2e²/h—matching theoretical predictions for QSH states where two spin-polarized channels counter-propagate along opposite edges of the device without dissipation.
The researchers confirmed these observations across various device geometries and probing configurations, ruling out conventional transport mechanisms. They also observed a large anomalous Hall (AH) effect—a separate spin-related quantum phenomenon—which persisted even at room temperature, further validating the presence of induced magnetic and spin-orbit interactions in the system.
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