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arXiv · 0802.4315

Giant Phonon-induced Conductance in Scanning Tunneling Spectroscopy of Gate-tunable Graphene

Yuanbo Zhang·Victor W. Brar·Feng Wang·Caglar Girit·Yossi Yayon·Melissa Panlasigui·Alex Zettl·Michael F. Crommie
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Abstract

The honeycomb lattice of graphene is a unique two-dimensional (2D) system where the quantum mechanics of electrons is equivalent to that of relativistic Dirac fermions. Novel nanometer-scale behavior in this material, including electronic scattering, spin-based phenomena, and collective excitations, is predicted to be sensitive to charge carrier density. In order to probe local, carrier-density dependent properties in graphene we have performed atomically-resolved scanning tunneling spectroscopy measurements on mechanically cleaved graphene flake devices equipped with tunable back-gate electrodes. We observe an unexpected gap-like feature in the graphene tunneling spectrum which remains pinned to the Fermi level (E_F) regardless of graphene electron density. This gap is found to arise from a suppression of electronic tunneling to graphene states near E_F and a simultaneous giant enhancement of electronic tunneling at higher energies due to a phonon-mediated inelastic channel. Phonons thus act as a "floodgate" that controls the flow of tunneling electrons in graphene. This work reveals important new tunneling processes in gate-tunable graphitic layers.

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Yuanbo Zhang, Victor W. Brar, Feng Wang, Caglar Girit, Yossi Yayon, Melissa Panlasigui, Alex Zettl, Michael F. Crommie. 2008-02-29. Giant Phonon-induced Conductance in Scanning Tunneling Spectroscopy of Gate-tunable Graphene. https://doi.org/10.1038/nphys1022

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