Voltage-Induced Rearrangements in Atomic-Size Contacts.

We study voltage-induced conductance changes of Pb, Au, Al, and Cu atomic contacts. The experiments are performed in vacuum at low temperature using mechanically controllable break junctions. We determine switching histograms, i.e., distribution functions of switching voltages and switching currents, as a function of the conductance. We observe a clear material dependence: Au reveals the highest and almost conductance-independent switching voltage, while Al has the lowest with a pronounced dependence on the conductance. The theoretical study uses density functional theory and a generalized Langevin equation considering the pumping of particular phonon modes. We identify a runaway voltage as the threshold at which the pumping destabilizes the atomic arrangement. We find qualitative agreement between the average switching voltage and the runaway voltage regarding the material and conductance dependence and contact-to-contact variation of the average characteristic voltages, suggesting that the phonon pumping is a relevant mechanism driving the rearrangements in the experimental contacts.

Nanosecond resistive switching in Ag/AgI/PtIr nanojunctions.

Nanometer-scale resistive switching devices operated in the metallic conductance regime offer ultimately scalable and widely reconfigurable hardware elements for novel in-memory and neuromorphic computing architectures. Moreover, they exhibit high operation speed at low power arising from the ease of the electric-field-driven redistribution of only a small amount of highly mobile ionic species upon resistive switching. We investigate the memristive behavior of a so-far less explored representative of this class, the Ag/AgI material system in a point contact arrangement established by the conducting PtIr tip of a scanning probe microscope. We demonstrate stable resistive switching duty cycles and investigate the dynamical aspects of non-volatile operation in detail. The high-speed switching capabilities are explored by a custom-designed microwave setup that enables time-resolved studies of subsequent set and reset transitions upon biasing the Ag/AgI/PtIr nanojunctions with sub-nanosecond voltage pulses. Our results demonstrate the potential of Ag-based filamentary memristive nanodevices to serve as the hardware elements in high-speed neuromorphic circuits.