The microscopic origin of graphene's near-ballistic transport is shown to be a remarkable insensitivity of electrons and holes to high-frequency optical phonon modes. Nonetheless, strong electron-phonon coupling persists with acoustic phonons, promoting coherent rather than diffusive transport.  Real-time, ab initio dynamic simulations provide evidence that charge carriers relax through the p-band within 100-200 fs.  High-density regions of the band structure facilitate nonadiabatic transitions induced by both acoustic and optical phonons.  Lattice defects cause electron and hole relaxation to slow to 400-700 fs.  The Stone-Wales bond rearrangement reduces the density of states throughout the band structure, reducing the overall electron-phonon resonances that drive diffusive, nonadiabatic processes.  Furthermore, additional phonon modes are introduced by the defect and couple strongly to electrons, decreasing low-energy coherent transport.  Synthesis of graphene in macroscopic quantities will undoubtedly yield lattice imperfections, where charge carriers slow down in response to broken electron-phonon resonances and unwieldy phonons.

Electronic speed traps in single layer graphene

244th National Meeting (2012)

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