Stiffnessometer: A Magnetic-Field-Free Superconducting Stiffness Meter And Its Application

We provide a detailed account for a method to measure superconducting stiffness rho(s), critical current density j(c), and coherence length xi, in one apparatus, without subjecting the sample to magnetic field or attaching leads. The method is based on the London equation j = rho(s)A, where j is the current density and A is the vector potential. Using a rotor free A and a measurement of j via the magnetic moment of a superconducting ring, we determine rho(s). By increasing A until the London equation fails we determine j(c) and xi. The method is sensitive to very small stiffness, which translates to penetration depth lambda less than or similar to 1 mm It is also sensitive to low critical current density j(c) similar to 10(3) A mm(-2) or long coherence length xi similar to 1 mu m. Naturally the method does not suffer from demagnetization factor complications, the presence of vortices, or out-of-equilibrium conditions. Therefore, the absolute values of the different parameters can be determined. We demonstrate the application of this method to La2-xSrxCuO4 with x = 0.17.