Determination of density of states of thin high-$T_c$ films by FET type   microstructures
  A simple electronic experiment with a field effect transistor type microstructure is suggested. The thin superconductor layer is the source-drain channel of the layered structure where an AC current is applied. It is necessary to measure the second harmonic of the source-gate voltage and third harmonic of the source-drain voltage. The electronic measurement can give the logarithmic derivative of the density of states which is an important parameter for fitting of parameters of the band structures. 
Todor Mishonov, Martin Stoev