Phonon switching and combined Fano-Rice effect in optical spectra of

 bilayer graphene

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Abstract

Recent infrared measurements of phonon peaks in gated bilayer graphene reveal two striking signatures of electron-phonon interaction: an asymmetric Fano lineshape and a giant variation of the peak intensity as a function of the applied gate voltage. In this Letter we provide a unified theoretical framework which accounts for both these effects and unveils the occurrence of a switching mechanism between the symmetric (\(E_g\)) and anti-symmetric (\(E_u\)) phonon mode as dominant channel in the optical response. A complete phase diagram of the optical phonon response is also presented, as a function of both the charge density and the bandgap.

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Field Effects on Optical Phonons in Bilayer Graphene

Tsuneya Ando, Mikito Koshino (2009)

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Observation of Distinct Electron-Phonon Couplings in Gated Bilayer Graphene

E. S. Alves, D. C. Elias, L Malard … (2008)

A Raman study of a back gated bilayer graphene sample is presented. The changes in the Fermi level induced by charge transfer splits the Raman G-band, hardening its higher component and softening the lower one. These two components are associated with the symmetric (S) and anti-symmetric vibration (AS) of the atoms in the two layers, the later one becoming Raman active due to inversion symmetry breaking. The phonon hardening and softening are explained by considering the selective coupling of the S and AS phonons with interband and intraband electron-hole pairs.

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Evidence for escape from adaptive conflict?

Todd Barkman, Jianzhi Zhang (2009)

Gene duplication is the primary source of new genes, but the molecular evolutionary mechanisms underlying functional divergence of duplicate genes are not well understood. Des Marais and Rausher argued that data from plant dihydroflavonol-4-reductase (DFR) genes support the model that gene duplication allows the escape from adaptive conflict (EAC) among several functions of a single-copy progenitor gene. As the authors indicated, the key predictions of EAC, in comparison to other models, are that (i) adaptive changes occur in both daughter genes after duplication, and (ii) these adaptive changes must improve ancestral functions. Furthermore, EAC indicates that (iii) the improvement of several ancestral functions is constrained before duplication, although this last point was not explicitly stated. Here we show that contrary to the predictions of EAC, only one of the duplicated DFR lineages exhibited adaptive sequence changes. Owing to the lack of information on enzyme concentrations we question the accuracy of enzyme activity comparisons, and it is thus not clear that any ancestral function has been improved in either lineage.