Clustering and conductance in breakage of sodium nanowires

We study the conductance during the elongation and breakage of Na nanowires described with the ultimate jellium model. A combined approach is used where the nanowire breakage is simulated self-consistently within the density-functional theory, and the wave packet propagation technique is applied for ballistic electron transport. For certain conditions the breakage of the nanowire is preceded by formation of clusters of magic size in the break junction. This affects the conductance G, in particular the shape of the G=3G0 to G=G0 (=2e2/h) step upon elongation. The observed trends can be explained as due to the transient trapping of ballistic electrons inside the cluster, leading to a resonant character of the electron transport through the break junction. The cluster-derived resonances appear as peak structures in the differential conductance which may serve as an experimental signature of clustering.