Contribution of Fluctuations of the Order Parameter to the Second Harmonic Generation in Two-Dimensional Monomolecular Superconductors

A theory of second harmonic generation in a two-dimensional superconductor in the fluctuation temperature regime has been developed within an approach based on the time-dependent Ginzburg–Landau equation. Expressions for the electric current that is induced by fluctuations of the order parameter and oscillates at the double frequency of the incident electromagnetic wave have been obtained. It has been shown that the effect has a significant singularity in temperature: the kinetic coefficients describing the second harmonic generation are inversely proportional to the square of the reduced temperature. The magnitude of the effect estimated for the two-dimensional superconductor based on a monomolecular molybdenum disulfide layer demonstrates the possibility of the experimental verification of the theory.