Optical imaging of strain-mediated phase coexistence during electrothermal switching in a Mott insulator

TL;DR

This study visualizes and analyzes the electrothermal resistive switching in V₂O₃ thin films, revealing the role of strain-induced heterogeneity and phase separation in the switching dynamics using microscopy and modeling.

Contribution

It provides direct optical visualization of strain-mediated phase coexistence during electrothermal switching in a Mott insulator, linking structural heterogeneity to switching behavior.

Findings

Reversible resistive switching visualized with high-resolution microscopy.

Formation of narrow metallic filaments during switching.

Heterogeneity and strain influence switching dynamics and filament morphology.

Abstract

Resistive-switching -- the current-/voltage-induced electrical resistance change -- is at the core of memristive devices, which play an essential role in the emerging field of neuromorphic computing. This study is about resistive switching in a Mott-insulator, which undergoes a thermally driven metal-to-insulator transition. Two distinct switching mechanisms were reported for such a system: electric-field-driven resistive switching and electrothermal resistive switching. The latter results from an instability caused by Joule heating. Here, we present the visualization of the reversible resistive switching in a planar V$_2$O$_3$ thin-film device using high-resolution wide-field microscopy in combination with electric transport measurements. We investigate the interaction of the electrothermal instability with the strain-induced spontaneous phase-separation in the V$_2$O$_3$ thin film at the Mott-transition. The photomicrographs show the formation of a narrow metallic filament with a minimum width $\lesssim$ 500\,nm. Although the filament formation and the overall shape of the current-voltage characteristics (IVCs) are typical of an electrothermal breakdown, we also observe atypical effects like oblique filaments, filament splitting, and hysteretic IVCs with sawtooth-like jumps at high currents in the low-resistance regime. We were able to reproduce the experimental results in a numerical model based on a two-dimensional resistor network. This model demonstrates that resistive switching, in this case, is indeed electrothermal and that the intrinsic heterogeneity is responsible for the atypical effects. This heterogeneity is strongly influenced by strain, thereby establishing a link between switching dynamics and structural properties.