Two-gap superconductivity seen in penetration-depth measurements ofLu2Fe3Si5single crystals

Abstract

A single crystal of superconducting ${\text{Lu}}_{2}{\text{Fe}}_{3}{\text{Si}}_{5}$ was studied using the tunnel-diode resonator technique in the Meissner and mixed states. The temperature dependence of the superfluid density provides strong evidence for two-gap superconductivity and indicates that there are nearly equal contributions from each gap having magnitudes of ${\ensuremath{\Delta}}_{1}/{k}_{B}{T}_{c}=1.86$ and ${\ensuremath{\Delta}}_{2}/{k}_{B}{T}_{c}=0.54$. In the vortex state, the pinning strength shows unusually strong temperature dependence and is nonmonotonic with the magnetic field (peak effect). The irreversibility line is sharply defined and quite distant from the ${H}_{c2}(T)$ line, which hints at enhanced vortex fluctuations in this two-gap system. Altogether, our findings from electromagnetic measurements provide strong support for the existence of two-gap superconductivity in ${\text{Lu}}_{2}{\text{Fe}}_{3}{\text{Si}}_{5}$, as previously suggested from specific-heat measurements.