Regensburg 2019 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 38: Methods in Computational Materials Modelling (methodological aspects, numerics)
MM 38.3: Talk
Thursday, April 4, 2019, 15:30–15:45, H44
On the negative differential conductance of single-wall carbon nanotubes from ab-initio quantum simulations — •Jaime Silva1, Bruce F. Milne1,2, and Fernando Nogueira1 — 1CFisUC, Department of Physics, University of Coimbra, Rua Larga, 3004-516 Coimbra, Portugal — 2Nano-Bio Spectroscopy Group, University of the Basque Country (UPV-EHU), Centro Joxe Mari Korta, Avenida de Tolosa, 72, 20018 Donostia-San Sebastian, Spain
Negative differential conductivity (NDC) is a current decrease when the voltage across certain materials is increased. It is important for oscillators, amplifiers, and fast switching devices. In this work, using real time quantum simulations, we show that this phenomenon occurs in isolated finite armchair single wall carbon nanotubes (SWCNT) without end contacts. For metallic SWCNT, like the armchair SWCNT, NDC due to electron transfer to secondary valleys is not expected to be observed, as a consequence of the two quantum channels at the Fermi energy that are available to conduction. The NDC is due to the finite nature of the SWCNT and the existence of excited states that are blocked, similarly to a Coulomb blockade system, thus preventing any further current flow. We also show that the SWCNT conductivity depends on its length and that the current flowing on the SWCNT behaves like a Bloch oscillation that is disrupted in the presence of a molecule, decreasing the conductivity, which explains the behaviour of SWCNT organic gas sensors.