Quasibound states and transport characteristics of Au chains with a substitutional S impurity.

Electronic transport properties of short gold atom chains with a single sulfur impurity were studied using density functional theory. It is found that the role of the impurity atom in the transport properties is twofold. First, it acts as a scattering center in the dominating 6s-orbital transmission channel and generally leads to a decrease of the transmission function in a wide energy region around the Fermi level. Second, it gives rise to a quasibound state manifesting as a peak near the Fermi level both in the partial density of states as well as in the transmission function. Because of the hybridization of the sulfur 3p and gold 5d orbitals in its formation, the quasibound state moves locally upward in the gold 5d transmission channel and brings about an enhancement of the transmission function in a narrow energy region near the Fermi level. The height of the peak of the quasibound state in the transmission function depends significantly on the position of the impurity in the chain and its energy varies with the bias voltage. The current-voltage (I-V) characteristics become asymmetric with a departure of the impurity from the central position in the chain and they are nonlinear for small values of the voltage (V < 0.1 V). It is proposed that a careful analysis of the I-V characteristics or the voltage dependence of the differential conductance may be used for unambiguous location of the light impurity in experiments with gold chains.