arXiv subjects

K. Hannewald

Publications and source records attributed to K. Hannewald.

2 recordsLinked to original sources

arXiv2008

Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene

We have measured a strictly linear pi-plasmon dispersion along the axis of individualized single wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single wall carbon nanotubes. Comparative ab initio studies on graphene based systems allow us to reproduce the different dispersions. This suggests that individualized nanotubes provide viable experimental access to collective electronic excitations of graphene, and it validates the use of graphene to understand electronic excitations of carbon nanotubes. In particular, the calculations reveal that local field effects (LFE) cause a mixing of electronic transitions, including the 'Dirac cone', resulting in the observed linear dispersion.

cond-mat.str-el↗

arXiv2004

Theory of small-polaron band conduction in ultrapure organic crystals

We present a novel theory of charge-carrier mobilities in organic molecular crystals of high purity. Our approach is based on Holstein's original concept of small-polaron bands but generalized with respect to the inclusion of nonlocal electron-phonon coupling. We derive an explicit expression for the mobilities as a function of temperature and, using ab-initio methods to obtain the material parameters, we demonstrate its predictive power by applying it to naphthalene. The results show a remarkably good agreement with experiments and provide new insight into the difference between electron and hole mobilities as well as their peculiar algebraic and anisotropic temperature dependences.

cond-mat.soft↗