Fig. 4: Influence of Peierls-like distortions on local currents.
From: Effect of Peierls-like distortions on transport in amorphous phase change devices
a Peierls-like distortion are heterogeneously distributed in the phase change device. Light colors depict atoms in less distorted environments (low r2/r1). b Current density in z-direction shows more and less conductive paths in the PCM. The current density was calculated for a single molecular dynamics snapshot at 250 K with a bias of 0.8 V, and is visualized for a slice through the device at x = 10. Red colors indicate current in the direction of transport, while black colors indicate reverse current due to backscattering. The diamonds indicate atomic positions. c Local density of states (LDOS) shows formation of layers in amorphous antimony due to confinement by the tungsten electrodes. Again, the LDOS at a bias of 0.8 V is calculated for a single snapshot at approximately 250 K from the ab-initio molecular dynamics simulation. The white line indicates the local electrostatic difference potential δVE, where the electrostatic difference potential at zero bias was subtracted. The values at z = 0 and z = l (with l the device length) correspond to the chemical potential of the respective electrode. Note that this potential is not completely flat in the contacts, probably due to the limited number of electrode layers and the limited number of k-points, which are both imposed by the computational demand of our simulations. d Antimony atoms in the center of the device are split into 4 × 4 groups. Average r2/r1 and average local current are calculated for each group as described in the main text. Only the first row of the 4 × 4 grid of groups is visible. Color indicates the average local current density in each group, where light and dark colors indicate high and low current density, respectively. e A large current density correlates with low values of distortion (r2/r1). The average current density in each group of atoms illustrated in (d) is calculated from ten different snapshots at 250 K, each 100 fs apart. Again, a bias of 0.8 V is used. The result is plotted versus the average distortion r2/r1 in each group. Error bars indicate the standard deviation.
