Researchers at The University of Manchester’s National Graphene Institute have demonstrated that electrons in graphene can be steered without scattering over microscopic distances, maintaining their spin coherence even at room temperature. This approach, detailed in the journal Physical Review X, utilizes principles of electron optics to refract electron spin, similar to bending light with a lens. The team employed transverse magnetic focusing to curve electron trajectories and reveal a clear spin signature, resolving three distinct peaks that confirm ballistic motion and spin transport. Manchester-based co-author Dr. Burrow said that the exciting aspect of this work is the ability to shape the path of electrons in graphene and simultaneously tune their spin behavior. He described it as using a set of lenses and mirrors for spin-polarized electrons, which could lead to lower-power electronics and quantum devices.
Graphene Enables Ballistic Electron Steering via Transverse Magnetic Focusing
This achievement overcomes a longstanding limitation in spintronics, where maintaining spin coherence typically requires extremely low temperatures, opening possibilities for more energy-efficient electronics and advanced quantum technologies. The team’s approach utilizes transverse magnetic focusing, refracting electron spin using principles analogous to light optics. The device, detailed in Physical Review X, employs ferromagnetic cobalt contacts to inject spin-polarized electrons into an encapsulated graphene channel; applying a magnetic field induces cyclotron orbits, curving the electron paths and allowing researchers to observe distinct signal peaks indicative of ballistic motion. Three such peaks were resolved in the study, and the height and sign of these peaks shifted based on the magnetic contact alignment, confirming the focused signal carried spin information. This demonstrates that spin is transported via ballistic trajectories, not through random scattering, which is vital for device functionality.
Researchers refined control by modulating the electron density in graphene via a back gate voltage, enhancing and even reversing the spin signal, before achieving transistor-like behavior without relying on spin-orbit interaction. Ivan Vera Marun explained that electron optics in graphene can do more than guide electrons; it can actively shape their paths in a spin-dependent manner. This new operational principle for spintronic components offers a promising alternative to traditional spin field-effect transistors, potentially leading to low-power, scalable spin-based technologies and future quantum systems.
Cobalt Contacts Induce Spin-Dependent Electron Optics & Gate-Voltage Control
This ballistic movement is revealed through transverse magnetic focusing (TMF) peaks, which provide a direct fingerprint of the electron’s trajectory. The device relies on ferromagnetic cobalt contacts to both inject and detect spin-polarized electrons at the edge of a graphene channel; when a magnetic field is applied, electrons curve into cyclotron orbits, and the team observed three distinct TMF peaks in their study. This tunability stems from a coupling between orbital motion and spin, induced by the cobalt contacts which create local charge-transfer doping and a proximity-exchange effect. This results in transistor-like behavior for spin, achieved without relying on spin-orbit coupling.
What’s exciting here is that we can shape the path of electrons in graphene and, at the same time, tune how their spins behave. It’s a bit like using a set of lenses and mirrors, but for spin-polarised electrons.
Room-Temperature Spin Coherence Confirms Potential for Spintronic Devices
This breakthrough, detailed in Physical Review X, depends on the ability to steer electrons across micrometre distances within the graphene channel, meaning they travel without scattering and maintain their spin information. This approach allows for precise control over electron spin without relying on spin-orbit interaction, a common requirement in many spintronic designs. The experimental setup involved ferromagnetic cobalt contacts used to inject and detect spin-polarized electrons, with a small out-of-plane magnetic field inducing cyclotron orbits. By modulating the voltage applied to a back gate, researchers could dramatically alter the spin signal, achieving transistor-like behavior for spin without introducing spin-orbit coupling.
We have shown that electron optics in graphene can do more than guide electrons, it can actively shape their paths in a spin-dependent manner. Being able to control spin in this way, using low-power and scalable materials, moves us closer to practical spin-based technologies and future quantum systems.
