Coupling of a high-energy excitation to superconducting quasiparticles   in a cuprate from Coherent Charge Fluctuation Spectroscopy
  Dynamical information on spin degrees of freedom of proteins or solids can be obtained by Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR). A technique with similar versatility for charge degrees of freedom and their ultrafast correlations could move forward the understanding of systems like unconventional superconductors. By perturbing the superconducting state in a high-Tc cuprate using a femtosecond laser pulse, we generate coherent oscillations of the Cooper pair condensate which can be described by an NMR/ESR formalism. The oscillations are detected by transient broad-band reflectivity and found to resonate at the typical scale of Mott physics (2.6 eV), suggesting the existence of a non-retarded contribution to the pairing interaction, as in unconventional (non Migdal-Eliashberg) theories. 
B. Mansart, J. Lorenzana, A. Mann, A. Odeh, M. Scarongella, M. Chergui   and F. Carbone
cond-mat.supr-con cond-mat.str-el