A team of researchers from the Universities of Manchester, Nottingham and Loughborough has discovered a quantum phenomenon that helps to understand the fundamental limits of graphene electronics.
Published in Nature Communications, the work describes how electrons in a single atomically-thin sheet of graphene scatter off the vibrating carbon atoms which make up the hexagonal crystal lattice.
By applying a magnetic field perpendicular to the plane of graphene, the current-carrying electrons are forced to move in closed circular "cyclotron" orbits. In pure graphene, the only way in which an electron can escape from this orbit is by bouncing off a "phonon" in a scattering event. These phonons are particle-like bundles of energy and momentum and are the "quanta" of the sound waves associated with the vibrating carbon atom. The phonons are generated in increasing numbers when the graphene crystal is warmed up from very low temperatures.
By passing a small electrical current through the graphene sheet, the team were able to measure precisely the amount of energy and momentum that is transferred between an electron and a phonon during a scattering event.
Their experiment revealed that two types of phonon scatter the electrons: transverse acoustic (TA) phonons in which the carbon atoms vibrate perpendicular to the direction of phonon propagation and wave motion (somewhat analogous to surface waves on water) and longitudinal acoustic (LA) phonons in which the carbon atoms vibrate back and forth along the direction of the phonon and the wave motion; (this motion is somewhat analogous to the motion of sound waves through air).
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