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:**Phonon dispersions generically display non-analytic points, known as Kohn anomalies, due to electron-phonon interactions. We analyze this phenomenon for a zone boundary phonon in undoped graphene. When electron-electron interactions with coupling constant $\beta$ are taken into account, one observes behavior demonstrating that the electrons are in a critical phase: the phonon dispersion and lifetime develop power law behavior with $\beta$ dependent exponents. The observation of this signature would allow experimental access to the critical properties of the electron state, and would provide a measure of its proximity to an excitonic insulating phase.Physical review. B, Condensed matter 09/2011; 85(8). · 3.77 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The fine structure of the Dirac energy spectrum in graphene induced by electron-optical phonon coupling is investigated in the portion of the spectrum near the phonon emission threshold. The derived new dispersion equation in the immediate neighborhood below the phonon threshold corresponds to an electron-phonon bound state. We find that the singular vertex corrections beyond perturbation theory increase strongly the electron-phonon binding energy. The predicted enhancement of the effective electron-phonon coupling can be measured using angle-resolved spectroscopy.Physical Review B 01/2012; 85:205453. · 3.66 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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