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Condensed Matter Seminars

ics Condensed Matter
Thursday, November 1, 2012
3:30 PM
Physics Building, Room 204
Note special time.
Note special room.
Avik Ghosh [Host: Bellave Shivaram]
University of Virginia
"Unconventional 'optics' with pseudospins in graphene: Metamaterials, Klein Tunneling and Subthermal switching"
ABSTRACT:
A major motivation for graphene based electronics lies in its photon-like bandstructure, which makes the electron effective mass vanishingly small and mobilities much larger than their silicon counterparts. In practice however, charge puddles wash out the Dirac points and produce quasi-Ohmic current-voltage characteristics, making it hard to switch graphene electrons or to saturate their currents. Long channel devices saturate through remote optical phonon scattering, but are almost immediately compromised by band-to-band tunneling. One can open a band-gap using quantization (e.g. nanoribbons), local strains, antidot arrays or transverse fields in bilayer geometries. But the broken symmetry invariably increases the mass of the electrons and compromises mobility. This trade-off seems fundamental.

The richness of graphene electronics lies not just in its photon like eigenspectrum, but in the symmetry of its eigenvalues, specifically, the pseudospins arising from its dimer basis sets. On the one hand quasi-momentum conservation at a PN junction generates electronic analogues of Snell's law such as focusing, total internal reflection, and even negative index Veselago 'lensing'. On the other hand, the orthogonality of its pseudospins leads to Klein/antiKlein tunneling in mono/bilayer graphene, for which there seem to be experimental evidence in close agreement with atomistic models for current flow. By solving the Landauer-Keldysh quantum kinetic equations, we show that such electron 'optics' and Klein tunneling can be used to design novel low power switches that can beat the Landauer- Boltzmann thermal limit, including reconfigurable logic, metal-insulator transition switches, electron collimators and pseudospintronic analogs of electro-optic modulators.

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