Measuring Superconducting Stiffness and Coherence of Magnetic Materials with zero-applied field

Superconducting (SC) stiffness  and coherence length  are usually measured by applying a magnetic field and measuring its penetration depth into a material  and the upper critical field . However, in magnetic materials, e.g. iron-based superconductors, this could lead to erroneous results since the field couples to the magnetic moments. To overcome this problem, we applied the Stiffnessometer technique to measure both quantities in FeSeTe. In this technique, one applies rotor-free vector potential  to a SC ring and measures with a SQUID the current density  via its magnetic moment  of the SC. , and  are determined from London’s equation  and its range of validity. Our results will be compared with theoretical expectations and other techniques. 

[1]. I. Mangel, I. Kapon, N. Blau, K. Golubkov, N. Gavish, and A. Keren, Phys. Rev. B 102, 024502 (2020).