Molecular wires acting as coherent quantum ratchets

J. Lehmann, S. Kohler, P. Hänggi, and A. Nitzan

Phys. Rev. Lett. 88, 228305 (2002)

Preprint: arXiv:cond-mat/0201480

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The effect of laser fields on electron transport through a molecular wire weakly coupled to two leads is investigated. The molecular wire acts as a coherent quantum ratchet if the molecule is composed of periodically arranged, asymmetric chemical groups. This setup presents a quantum rectifier with a finite dc response in the absence of a static bias. The nonlinear current is evaluated in closed form within the Floquet basis of the isolated, driven wire. The current response reveals multiple current reversals together with a nonlinear dependence on the amplitude and the frequency of the laser field. The current saturates for long wires at a nonzero value, while it may change sign upon decreasing its length.

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