  Photoelectron spectroscopy earlier probed oscillations in C60 valence
emissions, producing series of minima whose energy separation depends on the
molecular cavity. We show here that the quantum phase at these cavity minima
exhibits variations from strong electron correlations in C60, causing rich
structures in the emission time delay. Hence, these minima offer unique
spectral zones to directly explore multielectron forces via attosecond RABITT
interferometry not only in fullerenes, but also in clusters and nanostructures
for which such minima are likely abundant.
