Superconducting (SC) stiffness ρ_s and coherence length ξ are usually measured by applying a magnetic field and measuring its penetration depth into a material λ, and the upper critical field H_c2. 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 technique1 to measure both quantities in FeSeTe. In this technique one applies rotor-free vector potential A to a SC ring and measures with a SQUID the current density J via its magnetic moment M of the SC. ρ_s, and ξ are determined from London’s equation J=−ρ_sA and its range of validity as in Fig. 1. Our results will be compared with theoretical expectations and other techniques

Fig. 1: Magnetic moment of a ring-shaped FeSeTe superconductor as a result of current in an excitation coil, I_ec, which pierces the ring. In this configuration the ring does not experiences a magnetic field.

References

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