Large Negative Differential Resistance and Rectification from a Donor-σ-Acceptor Molecule in the Presence of Dissimilar Electrodes.

A multifunctional spin quantum device obtained by sandwiching 11-mercaptoundeca-2,4,8,10-tetraenenitrile, a donor-σ-acceptor molecule, between gold and iron electrodes is proposed. The device can act as a spin rectifier at lower bias and also exhibits negative differential resistance (NDR) after attaining a bias of 1.3 V. The rectification feature is quite prominent in the spin-up channel, with an appreciable rectification ratio of 68, whereas the NDR indicator, that is, the peak to valley ratio (≈10) of the current-voltage characteristics after 1.3 V, is also quite significant. To understand the origin of this in silico observation, nonequilibrium green's function based DFT calculations have been performed. Analyses reveal that both properties originate from the bias-independent energy offset between the frontier orbitals and electrode Fermi levels, popularly known as Fermi-level pinning. More precisely, rectification results from the Fermi-level pinning of the HOMO and LUMO with the gold and iron electrodes, respectively; the Fermi-level pinning forces a HOMO-LUMO crossover that helps to explain the origin of the NDR.