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

TL;DR

This study provides electromagnetic evidence for two-gap superconductivity in Lu$_2$Fe$_3$Si$_5$, revealing distinct gap magnitudes, complex vortex behavior, and enhanced fluctuations, supporting prior specific heat findings.

Contribution

It offers new electromagnetic measurements confirming two-gap superconductivity in Lu$_2$Fe$_3$Si$_5$, highlighting detailed vortex dynamics and fluctuations.

Findings

Strong evidence for two-gap superconductivity with distinct gap magnitudes

Unusual temperature dependence and non-monotonic field dependence of vortex pinning

Enhanced vortex fluctuations indicated by the irreversibility line behavior

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 $\Delta_1/k_BT_c=1.86$ and $\Delta_1/k_BT_c=0.54$. 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.