Comprehensive suppression of single-molecule conductance using destructive σ-interference

Marc H. Garner, Haixing Li, Yan Chen, Timothy A. Su, Zhichun Shangguan, Daniel W. Paley, Taifeng Liu, Fay Ng, Hexing Li, Shengxiong Xiao (), Colin Nuckolls (), Latha Venkataraman () and Gemma C. Solomon ()
Additional contact information
Marc H. Garner: University of Copenhagen
Haixing Li: Columbia University
Yan Chen: Shanghai Normal University
Timothy A. Su: Columbia University
Zhichun Shangguan: Shanghai Normal University
Daniel W. Paley: Columbia University
Taifeng Liu: Shanghai Normal University
Fay Ng: Columbia University
Hexing Li: Shanghai Normal University
Shengxiong Xiao: Shanghai Normal University
Colin Nuckolls: Shanghai Normal University
Latha Venkataraman: Columbia University
Gemma C. Solomon: University of Copenhagen

Nature, 2018, vol. 558, issue 7710, 415-419

Abstract: Abstract The tunnelling of electrons through molecules (and through any nanoscale insulating and dielectric material 1 ) shows exponential attenuation with increasing length 2 , a length dependence that is reflected in the ability of the electrons to carry an electrical current. It was recently demonstrated3–5 that coherent tunnelling through a molecular junction can also be suppressed by destructive quantum interference 6 , a mechanism that is not length-dependent. For the carbon-based molecules studied previously, cancelling all transmission channels would involve the suppression of contributions to the current from both the π-orbital and σ-orbital systems. Previous reports of destructive interference have demonstrated a decrease in transmission only through the π-channel. Here we report a saturated silicon-based molecule with a functionalized bicyclo[2.2.2]octasilane moiety that exhibits destructive quantum interference in its σ-system. Although molecular silicon typically forms conducting wires 7 , we use a combination of conductance measurements and ab initio calculations to show that destructive σ-interference, achieved here by locking the silicon–silicon bonds into eclipsed conformations within a bicyclic molecular framework, can yield extremely insulating molecules less than a nanometre in length. Our molecules also exhibit an unusually high thermopower (0.97 millivolts per kelvin), which is a further experimental signature of the suppression of all tunnelling paths by destructive interference: calculations indicate that the central bicyclo[2.2.2]octasilane unit is rendered less conductive than the empty space it occupies. The molecular design presented here provides a proof-of-concept for a quantum-interference-based approach to single-molecule insulators.

Date: 2018
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DOI: 10.1038/s41586-018-0197-9

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