Negative differential conductivity in liquid aluminum from real-time quantum simulations

The conduction of electricity in materials is usually described by Ohm’s law, which is a first order approximation to a more complex and non-linear behavior. It is well known that in some semiconductors, the conductivity, the constant that relates voltage and current, changes for high enough currents. In this work we predict for the first time that a metal, liquid aluminum, exhibits negative-differential conductivity, a non-linear effect where the current decreases as the applied voltage is increased. We observe this change in the conductivity for very high current densities of the order of 1012−1013 A∕cm2. Our predictions are based on a computational approach that can atomistically model, for the first time, non-linear effects in the conductivity from first principles by following in real-time the quantum dynamics of the electrons. From our simulations, we find that the change in the non-linear conductivity emerges from a competition between the current-induced accumulation of charge around the nuclei, which increases the scattering of the conduction electrons, and a decreasing ion-scattering cross-section at high currents. Our results illustrate how normal matter behaves under extreme fields that will become available from free electron lasers and other future experiments.