Manifestation of electron-electron interactions in time-resolved ultrafast pump-probe spectroscopy in C60:: Theory

The electron-electron interaction (EEI) is at the core of modern physics from high-temperature superconductivity to giant magnetoresistance. Nanostructures, in general, and C-60, in particular, open a new frontier for the study of the electron correlation effect in quasi-zero-dimensional materials. Here, a direct investigation of the time-resolved pump-probe signal in C-60 shows that the on-site electron-electron interaction manifests itself in two aspects in the early stage of ultrashort laser excitation. First, it pushes the signal peak to an earlier time delay for below-resonance excitation and narrows the peak-time change with probe detuning. Second, it shortens the quasiparticle lifetime and, if the interaction is strong enough, it diminishes the spike in the lifetime at resonance. These features are detectable experimentally, and the findings here suggest a different route to detect dynamical EEI in nanostructures.