From the point of view of statistical thermodynamics, a single particle doesn’t have a phase (state of matter), nor temperature.
What would happen if heat is transported to this single particle via radiation? How is this related to the same thing occurring for a mass of particles?
In addition, how can a single-molecule transistor, for example, depend on temperature via $f_{alpha} = left[ 1+exp left( frac{epsilon-mu_{alpha}}{k_B T} right) right]^{-1}$, if temperature is not even defined for a single molecule?