  Ultrafast phase transitions induced by femtosecond light pulses present a new
opportunity for manipulating the properties of materials. Understanding how
these transient states are different from, or similar to, their thermal
counterparts is key to determining how materials can exhibit properties that
are not found in equilibrium. In this paper, we reexamine the case of the
light-induced insulator-metal phase transition in the prototypical, strongly
correlated material VO$_2$, for which a nonthermal Mott-Hubbard transition has
been claimed. Here, we show that heat, even on the ultrafast timescale, plays a
key role in the phase transition. When heating is properly accounted for, we
find a single phase-transition threshold corresponding to the thermodynamic
structural insulator-metal phase transition, and we find no evidence of a
hidden transient Mott-Hubbard nonthermal phase. The interplay between the
initial thermal state and the ultrafast transition may have implications for
other transient states of matter.
