  We discuss the mechanisms behind the electrically driven insulator-metal
transition in single crystalline VO$_2$ nanobeams. Our DC and AC transport
measurements and the versatile harmonic analysis method employed show that
non-uniform Joule heating causes phase inhomogeneities to develop within the
nanobeam and is responsible for driving the transition in VO$_{2}$. A
Poole-Frenkel like purely electric field induced transition is found to be
absent and the role of percolation near and away from the electrically driven
transition in VO$_{2}$ is also identified. The results and the harmonic
analysis can be generalized to many strongly correlated materials that exhibit
electrically driven transitions.
