Correlative mapping of local hysteresis properties in VO$_2$

TL;DR

This paper introduces a novel optical microscopy method to map local hysteresis properties in VO$_2$, revealing detailed spatial and transition characteristics at micron scales, with implications for advanced electronic applications.

Contribution

The study develops a new microscopy technique to spatially resolve local hysteresis and transition properties in VO$_2$, providing unprecedented insights into phase transition behavior.

Findings

Revealed fractal electronic patterns on micron scales.

Identified regions with large or nearly absent local hysteresis.

Demonstrated high reproducibility of the transition cycle.

Abstract

We have developed a new optical microscopy technique able to track micron-sized surface clusters as temperature is varied. Potential candidates for study include phase separated metal-insulator materials, ferroelectrics, and porous structures. Several key techniques (including autofocus, step motor/cross correlation alignments, single-pixel thresholding, pair connectivity correlation length and image convolution) were implemented in order to obtain a time series of thresholded images. Here, we apply this new method to probe the archetypal phase separated insulator-metal transition in VO$_2$. A precise time and temperature series of the insulator-metal transition was achieved, allowing us to construct for the first time in this material spatial maps of the transition temperature T$_c$. These maps reveal multiple interesting features such as fractal electronic patterns on micron scales, regions of the sample with an extremely large or nearly absent local hysteresis, a positive correlation between the T$_c$ value and the hysteresis width $\Delta$T$_c$, and high cycle-to-cycle reproducibility of the transition. These maps also allow for the identification of individual pixels with unique transition characteristics. This unprecedented knowledge of the local properties of each spot along with the behavior of the entire network paves the way to novel electronics applications enabled by, {\em e.g.}, addressing specific regions with desired memory and/or switching characteristics, as well as detailed explorations of open questions in the theory of hysteresis.