Microwave emulations and tight-binding calculations of transport in polyacetylene

Abstract

International audienceA novel approach to investigate the electron transport of cis-and trans-polyacetylene chains in the single-electron approximation is presented by using microwave emulation measurements and tight-binding calculations. In the emulation we take into account the different electronic couplings due to the double bonds leading to coupled dimer chains. The relative coupling constants are adjusted by DFT calculations. For sufficiently long chains a transport band gap is observed if the double bonds are present, whereas for identical couplings no band gap opens. The band gap can be observed also in relatively short chains, if additional edge atoms are absent, which cause strong resonance peaks within the band gap. The experimental results are in agreement with our tight-binding calculations using the nonequilibrium Green's function method. The tight-binding calculations show that it is crucial to include third nearest neighbor couplings to obtain the gap in the cis-polyacetylene

Current Vortices in Aromatic Carbon Molecules

“…The nearest neighbor distance of the resonators is on average 14 mm, while their precise distance ratios reflect the interatomic distances found by the DFT optimization of the molecule. The coupling strength between neighboring resonators decays approximately exponentially, as shown previously [47,50]. Such an exponential decay is a realistic model for slightly varying carbon-carbon bond distances, as shown for deformed graphene [57].…”

“…Non-interacting quantum systems can be emulated by means of a network of dielectric microwave resonators [43][44][45][46][47][48][49][50]. Here, we use this technique to gain insight into the local current flow in aromatic carbon molecules.…”

“…The formal equivalence of the Helmholtz equation for electromagnetic waves and the non-interacting Schrödinger equation for quantum wave functions allows to emulate quantum systems in microwave cavities [40][41][42]. This idea can be used to realize tight-binding systems by networks of dielectric microwave resonators [43,44], as models for graphene [45][46][47][48][49] and molecules [50]. Here we apply this method to emulate the current flow in aromatic carbon molecules by means of a network of dielectric resonators, see Figure 2.…”

Transport gap engineering by contact geometry in graphene nanoribbons: Experimental and theoretical studies on artificial materials

“…Applying the techniques, developed to investigate the band structure of graphene 21,22 and to emulate relativistic systems 46,47 as well as molecular systems 24 , we have performed analogous experiments to study the coherent transport in graphene nanoribbons.…”

“…[21][22][23][24] Such experiments are well controlled and easy to perform (in comparison to experiments with real graphene or polyacetylene) and hence, offer a versatile tool to investigate in detail the properties of these systems. In this article, we study the ballistic single-electron transport through small graphene nanoribbons by microwave transmission experiments.…”