Two-fluid interpretation of the conductivity of clean BCS superconductors

A robust superconducting setup to probe the thermal Casimir effect

We describe a superconducting Casimir apparatus inspired by a recently proposed setup involving magnetic surfaces (Bimonte G 2014 Phys. Rev. Lett. 112 240401). The present setup consists of a superconducting Nb sphere and a flat gold plate including in its interior a superconducting Nb strip. The experimental scheme involves a differential measurement of the Casimir force at a point of the gold plate above the Nb strip and away from it. We show that similar to the previous setup, the superconducting system considered here implies widely different modulations of the Casimir force, depending on whether the thermal force is computed using the Drude or the plasma model, thus paving the way to an unambiguous discrimination between these alternative prescriptions.

Towards measuring variations of Casimir energy by a superconducting cavity

We consider a Casimir cavity, one plate of which is a thin superconducting film. We show that when the cavity is cooled below the critical temperature for the onset of superconductivity, the sharp variation (in the far infrared) of the reflection coefficient of the film engenders a variation in the value of the Casimir energy. Even though the relative variation in the Casimir energy is very small, its magnitude can be comparable to the condensation energy of the superconducting film, and this gives rise to a number of testable effects, including a significant increase in the value of the critical magnetic field, required to destroy the superconductivity of the film. The theoretical ground is therefore prepared for the first experiment ever aimed at measuring variations of the Casimir energy itself.