Paper detail

Nonlinear Meissner effect in Nb3Sn coplanar resonators

We investigated the nonlinear Meissner effect (NLME) in Nb$_3$Sn thin film coplanar resonators by measuring the resonance frequency as a function of a parallel magnetic field at different temperatures. We used low rf power probing in films thinner than the London penetration depth $λ(B)$ to significantly increase the field onset of vortex penetration and measure the NLME under equilibrium conditions. Contrary to the conventional quadratic increase of $λ(B)$ with $B$ expected in s-wave superconductors, we observed a nearly linear increase of the penetration depth with $B$. We concluded that this behavior of $λ(B)$ is due to weak linked grain boundaries in our polycrystalline Nb$_3$Sn films, which can mimic the NLME expected in a clean d-wave superconductor.