  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.
