Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 101: Transport - Poster Session

TT 101.35: Poster

Thursday, April 3, 2014, 15:00–19:00, P2

Phonon-drag thermopower in monolayer and bilayer graphene - significance of flexural phonons — •Eugen Wolf and Dietmar Lehmann — Institut für Theoretische Physik, TU Dresden, 01062 Dresden, Germany

Recent realizations of suspended monolayer graphene (MLG) and bilayer graphene (BLG) samples have enabled a direct probe of their intrinsic properties. It turns out that MLG and its bilayer possess high magnitudes of electron mobility and thermopower, thus promising attractive applications. A detailed study of the (intrinsic) scattering mechanisms, like electron-phonon-interaction, is therefore of large interest. A quite sensitive tool for investigating the coupling of electrons to acoustic phonons is the phonon-drag thermopower S^g. In free-standing graphene, electrons couple noticeably not only to in-plane longitudinal and transversal phonons, but also to out-of-plane (flexural) phonons. In our study, we indicate the contribution of flexural acoustic phonons to S^g in graphene for the first time. We have calculated S^g in doped, suspended MLG and BLG as function of temperature for different carrier densities by using a generalized Cantrell-Butcher formalism up to 2-phonon processes. Electron-phonon coupling by a screened deformation potential (proportional to the local contraction or dilatation of the lattice) as well as by an effective gauge field (induced by changes in bond length and bond angle between the carbon atoms) are included. We find that for reasonable coupling constants the electron scattering by out-of-plane phonons below 10 K cannot be neglected, especially for MLG.