Advanced Simulation of Conductance Histograms Validated through Channel-Sensitive Experiments on Indium Nanojunctions

We demonstrate a self-contained methodology for predicting conductance histograms of atomic and molecular junctions. Fast classical molecular-dynamics simulations are combined with accurate density functional theory calculations predicting both quantum transport properties and molecular-dynamics force field parameters. The methodology is confronted with experiments on atomic-sized indium nanojunctions. Beside conductance histograms the distribution of individual channel transmission eigenvalues is also determined by fitting the superconducting subgap features in the $I\mathrm{\text{−}}V$ curves. The remarkable agreement in the evolution of the channel transmissions demonstrates that the simulated ruptures are able to reproduce a realistic statistical ensemble of contact configurations, whereas simulations on selected ideal geometries show strong deviations from the experimental observations.

Figure 1

The top panels show demonstrative experimental conductance traces (a) and the conductance histogram (b) for indium junctions. The counts are normalized to the number of traces included. The bottom panels show examples of simulated conductance traces (c) and a theoretical conductance histogram (d). Note, that in (a) and (c) the zero point of the distance scale is arbitrarily chosen as the origin of the horizontal axis. Below the panels some atomic configurations are demonstrated (e1)–(e4), respectively, corresponding to the positions on the simulated traces signed by stars.

Figure 2

(a)–(d) The orange squares and blue circles, respectively, show the mean value of the experimental and theoretical channel transmissions. The solid red (dashed green) lines, respectively, show the channel transmissions during the stretching of an ideal dimer (monomer) configurations. The geometries of these ideal configurations are demonstrated in the insets. Panels (e) and (f) demonstrate the scattering wave function of the first two eigenchannels in a junction with an ideal dimer configuration ($G=1.18G_0$, ${\tau }_1=0.985$, ${\tau }_2=0.102$). The first channel (e) shows a $\sigma$-type, whereas the second channel (f) shows a $\pi$-type wave function at the central two atoms.

Figure 3

An experimentally measured conductance plateau (b) and the $I\mathrm{\text{−}}V$ curves recorded at three different points of the plateau (a1)–(a3). The fitted channel transmissions are given in the insets of panels (a1)–(a3), and demonstrated by red squares, blue stars, and orange triangles in panel (b) Panel (c) demonstrates a theoretical conductance trace (top black curve) together with the evolution of the channels transmissions (lower three curves, red, orange, and blue, respectively). Panels (d1)–(d3) demonstrate the junction geometries at the three points of the theoretical trace marked by stars.