Current rectification by molecules with asymmetric tunneling barriers

A simple experimentally accessible realization of current rectification by molecules (molecular films) bridging metal electrodes is described. It is based on the spatial asymmetry of the molecule and requires only one resonant conducting molecular level $(\pi$ orbital). The rectification, which is due to the asymmetric coupling of the level to the electrodes by tunnel barriers, is largely independent of the work function difference between the two electrodes. Results of extensive numerical studies of the family of suggested molecular rectifiers $\mathrm{HS}-({\mathrm{CH}}_2{)}_m-{\mathrm{C}}_6{\mathrm{H}}_4-({\mathrm{CH}}_2{)}_n-\mathrm{SH}$ are presented. The highest rectification ratio $\sim 500$ is achieved at $m=2\mathrm{}$ and $n=10.\mathrm{}$