Observation of reduction in Casimir force without change of dielectric permittivity

TL;DR

This study reports a significant reduction in the Casimir force after UV treatment of indium tin oxide without changing its dielectric permittivity, challenging existing theoretical models.

Contribution

It provides experimental evidence of Casimir force reduction independent of dielectric permittivity changes, suggesting a phase transition mechanism in indium tin oxide.

Findings

35% reduction in Casimir force observed after UV treatment

Reduction not accompanied by change in dielectric permittivity

Data aligns with phase transition from metallic to dielectric state

Abstract

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.