Insights into molecular conduction from I-V asymmetry
  We investigate the origin of asymmetry in the measured current-voltage (I-V) characteristics of molecules with no inherent spatial asymmetry. We establish that such molecules can exhibit asymmetric I-V characteristics due to unequal coupling with the contacts. In contrast with spatially asymmetric molecules, conduction takes place through essentially the same level in both bias directions. The asymmetry arises from a subtle difference in the charging effects, which can only be captured in a self-consistent model for molecular conduction. For HOMO-based conduction, the current is smaller for positive voltage on the stronger contact, while for LUMO conduction, the sense of asymmetry is switched. 
Avik W. Ghosh, Ferdows Zahid, Prashant S. Damle and Supriyo Datta