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Strong localization in defective carbon nanotubes

: Teichert, F.; Zienert, A.; Schuster, J.; Schreiber, M.

Verhandlungen der Deutschen Physikalischen Gesellschaft 50 (2015), Paper TT 88.4
ISSN: 0420-0195
ISSN: 0372-5448
Deutsche Physikalische Gesellschaft (DPG Jahrestagung) <79, 2015, Berlin>
Deutsche Physikalische Gesellschaft (DPG Frühjahrstagung) <2015, Berlin>
Fraunhofer ENAS ()

Carbon nanotubes (CNTs) are a prominent example for new materials in microelectronics, overcoming the miniaturization problem. So far CNTs cannot be grown or deposited in an ideal and reproducible way inside a device. As one consequence they contain defects.
The present work describes the transport properties of armchair CNTs with randomly positioned realistic defects, namely monovacancies and divacancies. The calculations are based on a fast, linearly scaling recursive Green's function formalism, allowing to treat large systems quantum-mechanically. The electronic structure is described by a density-functional-based tight-binding model.
The transmission spectrum of CNTs with single / many defects is studied. The influence of certain defect densities, the diameter of the CNT, and the temperature is investigated within a statistical analysis. It is shown that the system is in the regime of strong localization (i.e. Anderson localization), where the conductivity scales exponentially with the number of defects. This allows us to extract localization lengths, which depend on defect density, CNT diameter, and temperature. Finally, the correlation between the localization length and the single-defect conductance is shown.