Effect of gating on the transport properties of aSi4cluster

Abstract

The effect of gate voltage on the transport properties of ${\mathrm{Si}}_{4}$ cluster coupled with two atomic scale Al(100) electrodes has been investigated using a recently developed ab initio nonequilibrium Green's function technique. Motivated by a recent experiment [Champagne et al. Nano Lett. 5, 305 (2005)], the gating effect is probed in three cases with different contact distances. The equilibrium conductance is found to oscillate with the gate potential for all contact distances. We elucidate that this oscillatory behavior is very closely related to the variation of the system density of state at Fermi level. Moreover, we also demonstrate that the charge transfer is not the key factor to determine such a conductance oscillatory behavior. Through the analysis of the eigenchannel decomposition of the conductance, we suggest that gating does not change the eigenchannel number, and that the appearance of the conductance maximum results from the saturation of one or two eigenchannels. Even with the modification of gating, ${\mathrm{Si}}_{4}$ cluster still exhibits a negative differential resistance behavior. In particular, it also displays a negative transconductance behavior for a small fixed drain bias.