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The signature of chemical valence in the electrical conduction through a single-atom contact

Abstract

Fabrication of structures at the atomic scale is now possible using state-of-the-art techniques for manipulating individual atoms1, and it may become possible to design electrical circuits atom by atom. A prerequisite for successful design is a knowledge of the relationship between the macroscopic electrical characteristics of such circuits and the quantum properties of the individual atoms used as building blocks. As a first step, we show here that the chemical valence determines the conduction properties of the simplest imaginable circuit—a one-atom contact between two metallic banks. The extended quantum states that carry the current from one bank to the other necessarily proceed through the valence orbitals of the constriction atom. It thus seems reasonable to conjecture that the number of current-carrying modes (or ‘channels’) of a one-atom contact is determined by the number of available valence orbitals, and so should strongly differ for metallic elements in different series of the periodic table. We have tested this conjecture using scanning tunnelling microscopy and mechanically controllable break-junction techniques2,3 to obtain atomic-size constrictions for four different metallic elements (Pb, Al, Nb and Au), covering a broad range of valences and orbital structures. Our results demonstrate unambiguously a direct link between valence orbitals and the number of conduction channels in one-atom contacts.

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Figure 1: Typical conductance G as a function of distance, recorded during a continuous opening of the samples, for four different metals.
Figure 2: Measured current-voltage characteristics (plotting symbols) of five different configurations of a Pb sample at 1.5 K using STM, and best numerical fits (lines).
Figure 3: Localized orbitals model for electrical conduction through one-atom contacts.

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Acknowledgements

We thank D. Esteve and M. H. Devoret for discussions and C. Sürgers for graphics preparation; N.A. and G.R.B. thank S. Vieira for discussions and support. The work was supported in part by the Deutsche Forschungsgemeinschaft (DFG), the Spanish CICYT, “Stichting FOM” (NWO) and the Bureau National de Métrologie (BNM).

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Correspondence to Elke Scheer.

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Scheer, E., Agraït, N., Cuevas, J. et al. The signature of chemical valence in the electrical conduction through a single-atom contact. Nature 394, 154–157 (1998). https://doi.org/10.1038/28112

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