Conductance of a Freestanding Molecular Wire*

Measuring the electrical conductance along a molecule in a reproducible way is an extremely difficult task, as it requires an atomic scale control of the contact formation between the molecule and the electrodes. In this work, we have succeed in controllably forming a contact between the tip of a STM and a freestanding molecular wire, which is placed vertically on the substrate using a platform molecule. The measured complex variation of the conductance with electrode separation is rationalized using DFT transport calculations.[1] At large electrode separation, the transport properties are controlled by the deformation of the molecule, which gives rise to a symmetry mismatch between the tip and molecule orbitals and, hence, to a decrease in the conductance. At closer distances, a covalent bond is formed between the Au tip and a triple CC bond, inducing a significant change of the electronic spectrum and an order of magnitude increase in the conductance. Therefore, by a tip-controlled reversible bond formation or rupture we are able to switch the current on or off. [1]T. Jasper-Tönnies, A. Garcia-Lekue, et al. Phys. Rev. Lett. 119, 066801 (2017).