  Additional information is provided on the effect of the significant (up to
35%) reduction in the magnitude of the Casimir force between an Au-coated
sphere and an indium tin oxide film which was observed after UV treatment of
the latter. A striking feature of this effect is that the reduction is not
accompanied with a corresponding variation of the dielectric permittivity, as
confirmed by direct ellipsometry measurements. The measurement data are
compared with computations using the Lifshitz theory. It is shown that the data
for the untreated sample are in a very good agreement with theory taking into
account the free charge carriers in the indium tin oxide. The data for the
UV-treated sample exclude the theoretical results obtained with account of free
charge carriers. These data are found to be in a very good agreement with
theory disregarding the free charge carriers in an indium tin oxide film. A
possible theoretical explanation of our observations as a result of phase
transition of indium tin oxide from metallic to dielectric state is discussed
in comparison with other related experiments.
