Manchester Team Achieves Ballistic Control of Electron Spin in Graphene

In a pioneering breakthrough at The University of Manchester’s National Graphene Institute, researchers have succeeded in precisely steering electrons through ultra-clean graphene while preserving their spin coherence intact. This landmark achievement paves the way for the next generation of low-power electronic devices and advances toward quantum computing technologies. The findings, recently published in the prestigious journal Physical Review X, demonstrate the ability to maintain ballistic electron motion over micrometre distances in graphene at low temperatures, with spin coherence persisting up to ambient conditions—a feat that has long been a sought-after goal in spintronics and quantum device engineering.

Graphene’s exceptional electrical properties make it a prime candidate for hosting spin-polarized electron transport. However, maintaining both ballistic motion and spin information during electron travel is a significant challenge, primarily because scattering events typically disrupt electron paths and spin orientation. The research team applied a sophisticated technique known as transverse magnetic focusing (TMF) to overcome this hurdle. TMF guides electrons in curved trajectories reminiscent of light rays passing through optical lenses, hence allowing the direct observation and control of spin-polarized electron paths in a solid-state medium.

The essence of this method involves injecting spin-polarized electrons into the graphene channel via engineered ferromagnetic cobalt contacts. These contacts serve the dual purpose of spin injection and detection, situated strategically at the edges of an encapsulated graphene device. When subjected to a strategic out-of-plane magnetic field, electrons follow cyclotron orbits—circular paths determined by the balance of their momentum and the magnetic force. By tuning the magnetic field, researchers could manipulate these orbits so that electrons land precisely on the detector contacts, generating distinct peaks in detected signal amplitude known as TMF peaks. Each peak acts as a fingerprint, indicating highly ballistic electron transport and revealing the spin-dependent nature of their motion.

One of the remarkable discoveries in this study is how the morphology and amplitude of TMF peaks depend sensitively on the alignment of the magnetic contacts—providing unambiguous evidence that spin information is preserved and transported via ballistic electron trajectories, not through diffusive scattering mechanisms. This spin-dependent electron optics creates a transformative platform where electrons can be treated like photons in a carefully arranged optical system, but with their spin degree of freedom fully exploited and tunable.

Key to the functionality of this device is the control afforded by varying the back gate voltage. By applying different voltages, the electron density within the graphene channel can be modulated finely, which in turn drastically changes the observed spin signals. In some configurations, this tuning enhanced spin signals compared to conventional spin-valve measurements. Conversely, the polarity of the spin signal could be inverted, offering a transistor-like switch for spin currents. This level of control stems from a profound interplay between the electron’s orbital motion and spin, mediated by proximity effects from the ferromagnetic contacts. These contacts induce local charge transfer and proximity exchange interactions, creating a magnetic character adjacent to the graphene edges. As a result, ballistic electrons traveling from these “magnetized” regions into the pristine graphene channel carry spin-dependent information orchestrated purely through electron optics.

Importantly, this approach circumvents the need to invoke strong spin–orbit interaction—which is usually weak in graphene—thus preserving its intrinsic qualities and enhancing device scalability. Unlike conventional spintronic devices that rely on heavy materials or structures with intrinsic spin–orbit coupling, this electron-optics-based mechanism offers a more straightforward and tunable route to spin control. The ability to engineer spin behavior through ballistic electron trajectories rather than modifying the material’s fundamental properties is a game-changing paradigm.

From an applications standpoint, the team observed robust ballistic behavior at low temperatures around 25 K, and even more impressively, quasi-ballistic transport persisted at room temperature. The sustained sensitivity of TMF peaks to spin polarization at these elevated temperatures signals the viability of utilizing this mechanism in real-world devices without the impractical need for extreme cooling. This breakthrough opens exciting prospects for spin-based transistors, spin logic gates, and quantum bits, promising lower power consumption, faster operation, and enhanced integration with existing semiconductor technologies.

The operational principle established by this research mirrors some conceptual aspects of the long-theorized Datta–Das spin field-effect transistor but achieves actual spin modulation through the lens of electron optics rather than relying on elusive spin–orbit interactions. By shaping electron trajectories and manipulating spin states as we would with photons in complex optical systems, a new architecture for spintronic devices emerges—flexible, tunable, and highly efficient.

Dr. Daniel Burrow, a co-author of the study, underscores the significance of these advancements by comparing their method to a sophisticated set of lenses and mirrors designed for spin-polarized electrons. The capacity to control spin simultaneously with electron pathways, without the addition of spin–orbit coupling, unlocks unprecedented routes toward practical, scalable spintronics.

Further insights were provided by Dr. Ivan Vera Marun, another co-author, who highlighted that the observed electron optics goes beyond passive guidance—it actively modulates spin-dependent pathways. This level of control through low-power, scalable graphene devices brings us closer to the realization of spin-based quantum technologies that can seamlessly integrate with current technology infrastructures.

In summary, this landmark research presents a new frontier in manipulating spin-coherent ballistic transport in graphene via electron optics. By employing transverse magnetic focusing and exploiting ferromagnetic contact-induced doping and proximity effects, the study creates a promising spin-valve system exhibiting transistor-like characteristics. It heralds a future in which electron spin, rather than charge alone, can be exploited to design fast, low-energy, and quantum-compatible devices, fundamentally altering how information processing technologies operate.

News Publication Date: 7-May-2026

Web References:
DOI: 10.1103/nz6m-kb4l

Keywords

Graphene, Spintronics, Ballistic electron transport, Spin coherence, Electron optics, Transverse magnetic focusing, Spin field-effect transistor, Proximity exchange effect, Ferromagnetic contacts, Quantum devices, Low-power electronics, Spin-polarized electrons