Article

# Chirality-induced dynamic kohn anomalies in graphene.

Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.

Physical Review Letters (Impact Factor: 7.73). 09/2008; 101(6):066401. DOI: 10.1103/PhysRevLett.101.066401 Source: PubMed

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**ABSTRACT:**We develop a theory for the energy relaxation of hot Dirac fermions in graphene. We obtain a generic expression for the energy relaxation rate due to electron-phonon interaction and calculate the power loss due to both optical and acoustic phonon emission as a function of electron temperature $T_{\mathrm{e}}$ and density $n$. We find an intrinsic power loss weakly dependent on carrier density and non-vanishing at the Dirac point $n = 0$, originating from interband electron-optical phonon scattering by the intrinsic electrons in the graphene valence band. We obtain the total power loss per carrier $\sim 10^{-12} - 10^{-7} \mathrm{W}$ within the range of electron temperatures $\sim 20 - 1000 \mathrm{K}$. We find optical (acoustic) phonon emission to dominate the energy loss for $T_{\mathrm{e}} > (<) 200-300 \mathrm{K}$ in the density range $n = 10^{11}-10^{13} \mathrm{cm}^{-2}$. Comment: 5 pagesPhysical review. B, Condensed matter 12/2008; · 3.77 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We present a first-principles study of the electron-phonon (e-ph) interactions and their contributions to the linewidths for the optical-phonon modes at Γ and K in one-layer to three-layer graphene. It is found that, due to the interlayer coupling and the stacking geometry, the high-frequency optical-phonon modes in few-layer graphene couple with different valence and conduction bands, giving rise to different e-ph interaction strengths for these modes. Some of the multilayer optical modes derived from the Γ-E2g mode of monolayer graphene exhibit slightly higher frequencies and much reduced linewidths. In addition, the linewidths of K-A1′ related modes in multilayers depend on the stacking pattern and decrease with increasing layer numbers.Physical review. B, Condensed matter 02/2009; 79(11). · 3.77 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Dirac electrons in graphene in the presence of Coulomb interactions of strength $\beta$ have been shown to display power law behavior with $\beta$ dependent exponents in certain correlation functions, which we call the mass susceptibilities of the system. In this work, we first discuss how this phenomenon is intimately related to the excitonic insulator transition, showing the explicit relation between the gap equation and response function approaches to this problem. We then provide a general computation of these mass susceptibilities in the ladder approximation, and present an analytical computation of the static exponent within a simplified kernel model, obtaining $\eta_0 =\sqrt{1-\beta/\beta_c}$ . Finally we emphasize that the behavior of these susceptibilities provides new experimental signatures of interactions, such as power law Kohn anomalies in the dispersion of several phonons, which could potentially be used as a measurement of $\beta$.Solid State Communications 02/2012; 152(15). · 1.53 Impact Factor

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