Oscillatory Conductance of Carbon-Atom Wires

The conductance of carbon-atom chains is found from first-principles calculations to vary in an oscillatory manner as the number of carbon atoms is increased, with odd-numbered chains having a lower resistance than even-numbered chains. This finding is explained in terms of the electronic structure of the free chains and its modification by interaction with the metal electrodes: the critical factor is the density of states at the Fermi level of the combined electrode–atomic-wire system. Stronger electrode–atomic-wire coupling, i.e., shorter metal-carbon distance, does not necessarily imply a higher conductance.