Workshop "NMR, µSR, Mössbauer spectroscopies in the study of Fe-based and other unconventional high-Tc superconductors"
Charge fluctuation spectroscopy of superconductors, the charge analog of NMR
José Lorenzana, Universitá “La Sapienza” di Roma, Italy
It has been recently demonstrated that a pump pulse can generate coherent charge fluctuations in a superconductor through a stimulated Raman process  paving the way to a new technique, Coherent Charge Fluctuation Spectroscopy (CCFS), to investigate pairing interactions and manipulate the superconducting wave function. We will present the basic phenomena involved and show how the technique bears a strong analogy with nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). The reflectivity of the system gets modulated by the coherent charge fluctuation of the condensate. A resonance at the Mott scale (2.6eV) allows to identify a high-energy excitation which is coupled to the superconducting quasiparticles which suggest that non-retarded interactions are involved in the pairing as suggested by unconventional theories of superconductivity.
 B. Mansart et al., Proc. Natl. Acad. Sci. 110, 4539 (2013); J. Lorenzana et al., Europ. Phys. J ST 222, 1223 (2013).