Effect of pulse duration on current-induced selective oxygen migration in high-Tc superconductors

TL;DR

This study investigates how pulse duration affects current-induced oxygen migration in YBCO superconductors, revealing a transition from thermally driven to athermal electromigration at very short pulses, with implications for memristor operation.

Contribution

It provides the first analysis of pulse length effects on electromigration onset in YBCO, highlighting the shift to athermal processes at sub-10 microsecond pulses.

Findings

Shorter pulses increase the electromigration threshold current.

Temperature decreases with shorter pulse durations, reducing thermal effects.

Electromigration becomes predominantly athermal below ~10 microseconds.

Abstract

High current densities can induce the directional diffusion of atoms in metallic films. In YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO), this electromigration process selectively acts on oxygen atoms lying in the Cu-O chains, permitting to vary the oxygen concentration in a targeted spot of high current density. This approach has proven successful in mapping the phase diagram of the material as a function of carrier concentration or as a way to manufacture memristive devices owing to its reversibility under small bipolar excitations. Thus far, most of the investigations have been limited to pulsed excitation with current/voltage pulses on a millisecond or longer scale, for which thermal effects undeniably influence the process. In the present work, we explore the impact of pulse length $\delta t$ on the onset current of electromigration, $I_{\text{EM}}$, of YBCO bridges, covering the range from 200 ns to 1 ms. As $\delta t$ decreases below $\sim 10~\mu$s, $I_{\text{EM}}$ exhibits a rapid increase. Analytical and numerical estimates of the local temperature show that as pulses shorten, the temperature decreases, making the electromigration process more athermal. These findings are relevant for the operation of memristors and should be taken into account when describing the effects of thermomagnetic instabilities in thin films.