How Deep Does a Magnetic Field Penetrate into Fe-based Superconductors?

Electronic Anisotropy

Magnetic field is expelled from the bulk of a superconductor and only remains present in a surface layer called London penetration depth, λ. Precision measurements of this quantity provide insight into the structure of the superconducting gap and, ultimately, into the mechanism of superconductivity. Ames laboratory has a unique technique based on a self-resonating tunnel-diode resonator (TDR) that allows for precision measurements of the temperature-induced changes in the penetration depth that has already led to numerous discoveries in various superconductors. However, measurements of the absolute values are needed to answer fundamental questions related to the role of magnetism - a key question in Fe-based superconductors.

This research is a result of a long project that developed a new technique to measure the absolute value of λ. Scientists observed a dramatic increase in the penetration depth on the part of the phase diagram where itinerant magnetism competes with superconductivity for the same pool of conduction electrons. These measurements have also allowed the determination of the absolute density of Cooper pairs, which indicates developing anisotropy of the superconducting gap toward the edges of the superconducting dome.

 

Contact: R. Prozorov, prozorov@ameslab.gov

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