  We report pair distribution function measurements of the iron-based
superconductor FeSe above and below the structural transition temperature.
Structural analysis reveals a local orthorhombic distortion with a correlation
length of about 4 nm at temperatures where an average tetragonal symmetry is
observed. The analysis further demonstrates that the local distortion is larger
than the distortion at temperatures where the average observed symmetry is
orthorhombic. Our results suggest that the low-temperature macroscopic nematic
state in FeSe forms from an imperfect ordering of orbital-degeneracy-lifted
nematic fluctuations which persist up to at least 300 K.
