Two-gap superconductivity in single crystal Lu₂Fe₃Si₅ from penetration depth measurements

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Single crystal of Lu₂Fe₃Si₅ 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 Δ₁/kBTc=1.86 and Δ₁/kBTc=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 Hc₂(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 Lu₂Fe₃Si₅ previously suggested from specific heat measurements.