Graphene enables spin-preserving ballistic electron transport for future spintronics

University of Manchester researchers have shown that electrons in ultra-clean graphene can be steered with high precision while keeping their spin information intact, a key requirement for future low power electronics and quantum devices. The team demonstrates how electrons can travel ballistically, i.e. without experiencing any scattering or resistance, over micrometer distances in graphene at low temperature and maintain spin coherence all the way up to room temperature. By using a technique known as transverse magnetic focusing (TMF), they were able to bend electron trajectories like light rays traversing a lens and show that these curved paths carry a clear spin signature. Manchester-based Co-author Dr. Daniel Burrow said: “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-polarized electrons. This opens a practical way to control spin without needing strong spin–orbit interaction in the material.”The team’s graphene device uses ferromagnetic cobalt contacts to inject and detect spin-polarized electrons at the edge of an encapsulated graphene channel. When a small out-of-plane magnetic field is applied, electrons paths curve into so-called cyclotron orbits. If those orbits are the right size, they land directly on the detector contact producing distinct peaks in signal at specific magnetic fields. These TMF peaks provide a direct fingerprint of ballistic electron motion. Three such peaks were resolved in the study.Crucially, the height and sign of these TMF peaks changed depending on the alignment of the magnetic contacts, showing that the focused signal carried spin information. This confirms that ballistic trajectories, rather than diffusive scattering processes, were responsible for transporting spin across the device.By varying the voltage applied to the back gate, which tunes the density of electrons in graphene, the researchers could modulate the spin signal dramatically. In some conditions, they enhanced the signal relative to standard nonlocal spin-valve measurements. In others, they could reverse its polarity altogether. University of Manchester researchers have shown that electrons in ultra-clean graphene can be steered with high precision while keeping their spin information intact, a key requirement for future low power electronics and quantum devices. The team de... [3574 chars]