Near field optical visualization of the nanoscale phase percolation dynamics of a VO2 oscillator.

Self-sustained resistance oscillation in vanadium dioxide (VO2) are of significant interest for phase-based information encoding applications. However, the underlying mechanism behind the current-induced insulator-to-metal phase oscillation and its spatiotemporal dynamics remains elusive. Here, using high-resolution near-field optical imaging, we uncover distinct current-induced phase transition pathways in VO2(001) thin films. We show that the formation of a persistent metallic patch within active region, defined as the area between the electrodes in a two-terminal model device serves as a prerequisite for oscillations. In this region, transient conductive filaments as narrow as 140 nm bridge the patch to the electrodes. Additionally, we observe oscillation modulated optical signals that extend well beyond the active region, providing clear evidence for a mechanism that would couple neighboring oscillators. Our work provides direct insight into the percolation dynamics that controls the oscillatory state of a VO2 oscillator, paving the way to optimally designed oxide electronics.