Two-gap superconductivity in single crystal Lu${}_2$Fe${}_3$Si${}_5$ from penetration depth measurements

Abstract

Single crystal of Lu${}_2$Fe${}_3$Si${}_5$ was studied with the tunnel-diode resonator technique in Meissner and mixed states. Temperature dependence of the superfluid density provides strong evidence for the two-gap superconductivity with almost equal contributions from each gap of magnitudes $\hat{I}{”}_1/k_B{T}_c=1.86$ and $\hat{I}{”}_1/k_B{T}_c=0.54$. In the vortex state, pinning strength shows unusually strong temperature dependence and is non-monotonic with the magnetic field (peak effect). The irreversibility line is sharply defined and is quite distant from the $H_{c2}(T)$, which hints on to enhanced vortex fluctuations in this two-gap system. Altogether our findings provide strong electromagnetic - measurements support to the two-gap superconductivity in Lu${}_2$Fe${}_3$Si${}_5$ previously suggested from specific heat measurements.