Microscopic study of the impurity effect in the kagome superconductor La(Ru$_{1-x}$Fe$_{x}$)$_{3}$Si$_{2}$

TL;DR

This study investigates how magnetic impurities affect the superconducting properties of a kagome-lattice superconductor, revealing unconventional behavior and gap nodes induced by Fe doping, which provides new insights into the microscopic mechanisms of superconductivity.

Contribution

It demonstrates the impact of Fe impurities on the superconducting gap structure and superfluid density in La(Ru$_{1-x}$Fe$_{x}$)$_{3}$Si$_{2}$, highlighting tunability and unconventional superconductivity in kagome lattices.

Findings

Superconducting critical temperature $T_c$ is strongly suppressed by Fe doping.

Superfluid density correlates with $T_c$, indicating unconventional superconductivity.

Fe doping induces nodes in the superconducting gap at low concentrations.

Abstract

We report on the effect of magnetic impurities on the microscopic superconducting (SC) properties of the kagome-lattice superconductor La(Ru$_{1-x}$Fe$_{x}$)$_{3}$Si$_{2}$ using muon spin relaxation/rotation. A strong suppression of the superconducting critical temperature $T_{\rm c}$, the SC volume fraction, and the superfluid density was observed. We further find a correlation between the superfluid density and $T_{\rm c}$ which is considered a hallmark feature of unconventional superconductivity. Most remarkably, measurements of the temperature-dependent magnetic penetration depth ${\lambda}$ reveal a change in the low-temperature behavior from exponential saturation to a linear increase, which indicates that Fe doping introduces nodes in the superconducting gap structure at concentrations as low as $x=$~0.015. Our results point to a rare example of unconventional superconductivity in the correlated kagome lattice and accessible tunability of the superconducting gap structure, offering new insights into the microscopic mechanisms involved in superconducting order.