V. M. Kovalev and I. G. Savenko
We propose to employ an optical spectroscopy technique to monitor the superconductivity and properties of superconductors in the fluctuating regime. This technique is operational close to the plasmon resonance frequency of the material, and it intimately connects with the superconducting fluctuations slightly above the critical temperature Tc. We find the Aslamazov-Larkin corrections to ac linear and dc nonlinear electric currents in a generic two-dimensional superconductor exposed to an external longitudinal electromagnetic field. First, we study the plasmon resonance of normal electrons near Tc, taking into account their interaction with superconducting fluctuations, and show that fluctuating Cooper pairs reveal a redshift of the plasmon dispersion and an additional mechanism of plasmon scattering, which surpasses both the electron-impurity and the Landau dampings. Second, we demonstrate the emergence of a drag effect of superconducting fluctuations by the external field resulting in considerable, experimentally measurable corrections to the electric current in the vicinity of the plasmon resonance.
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