Casimir interaction at liquid nitrogen temperature: Comparison between experiment and theory

We have measured the normalized gradient of the Casimir force between Au-coated surfaces of the sphere and the plate and equivalent Casimir pressure between two parallel Au plates at T = 77 K. These measurements have been performed by means of dynamic force microscope adapted for operating at low temperatures in the frequency shift technique. It was shown that the measurement results at T = 77 K are in a very good agreement with those at T = 300 K and with computations at T = 77 K using both theoretical approaches to the thermal Casimir force proposed in the literature. No thermal effect in the Casimir pressure was observed in the limit of experimental errors with the increase of temperature from T = 77 to 300 K. Taking this into account, we have discussed the possible role of patch potentials in the comparison between measured and calculated Casimir pressures.