Regular Atomic Narrowing of Ni, Fe, and V Nanowires Resolved by Two-Dimensional Correlation Analysis

We present a novel statistical method for the study of stable atomic configurations in breaking nanowires based on the 2D cross-correlation analysis of conductance versus electrode separation traces. Applying this method, we can clearly resolve the typical evolutions of the conductance staircase in some transition metal nanojunctions (Ni, Fe, V) up to high conductance values. In these metals our analysis demonstrates a very well ordered atomic narrowing of the nanowire, indicating a very regular, stepwise decrease of the number of atoms in the minimal cross section of the junction, in contrast to the majority of the metals. All these features are hidden in traditional conductance histograms.

Figure 1

Measurements on Au junctions: (a) representative conductance vs electrode separation traces; (b) histogram for the middle trace on panel (a); (c) histogram for the whole data set including 5000 traces; (d) 2D correlation histogram, $C_{i,j}$ for the same data set. (e) Illustration for slant plateaus and neighboring jumps, respectively, being responsible for positively correlated areas at the diagonal of the correlation plot and the neighboring negatively correlated region.

Figure 2

Measurements on Ni junctions. (a) Bottom area graph shows the conductance histogram for the whole data set including 5000 traces. The line graphs show conditional histograms for different subsets of the traces (see text). Horizontal dashed lines show the zero values of the histograms, vertical dashed lines indicate the peak positions in the middle conditional histogram. (b) 2D correlation histogram for the whole data set. (c) Representative conductance traces. (d) Illustration for the correlated shifting of plateaus.

Figure 3

Simulations for stripes. (a) Experimental data on Ni with two simplified fits. (b) More advanced simulations. (See text and supplementary material for details [15]).