Stiffness and coherence length measurements of ultra-thin superconductor, and implications to layered superconductors

Abstract

Based on the London equation, we use a rotor-free vector potential $\mathbf{A}$, and current measurements by a SQUID, to determine the superconducting Pearl length $\hat{I}›$, and coherence length $\hat{I}¾$, of ultra-thin, ring shaped, MoSi films, as a function of thickness $d$ and temperature $T$. We find that $\hat{I}¾$ is a function of $d$ with a jump at $\hat{I}¾\sim d\sim 5$nm. At base temperature the superconducting stiffness, defined by $1/\hat{I}{»}^2=1/(\hat{I}›d)$, is an increasing function of $T_c$. Similar behavior, known as the Uemura plot, exist in bulk layered superconductors, but with doping as an implicit parameter. We also provide the critical exponents of $\hat{I}›(T)$.

7 pages, 7 figures