Current-voltage characteristics through a single light-sensitive molecule

A light-sensitive molecular switch based on single azobenzene molecule has been proposed recently [ C. Zhang, M. H. Du, H. P. Cheng, X. G. Zhang, A. E. Roitberg and J. L. Krause Physical Review Letters 92 158301 (2004)]. Here we investigate the stability of the molecular switch under finite bias. Using a first-principles method that combines the nonequilibrium Green’s function technique and density functional theory, we compute the current-voltage curves for both trans and cis configurations of the azobenzene molecule connected to two gold leads between bias voltages of 0 and 1 V. We find that the current through the trans configuration is significantly higher than that through the cis configuration for most biases, suggesting that the molecular switch proposed previously is stable under the finite bias. A negative differential conductance (NDR) is found for the cis configuration at 0.8 V. Analysis of the band structure of the leads and the molecular states reveals that the transmission through the highest occupied molecular orbital state of the molecule is suppressed significantly at this bias voltage, which causes the NDR.