Superconducting Gap Structure of Filled Skutterudite LaOs$_4$As$_{12}$ Compound through $\mu$SR Investigations

TL;DR

This study investigates the superconducting gap structure of LaOs$_{4}$As$_{12}$ using $$SR and specific heat measurements, revealing a fully gapped, time-reversal symmetric superconducting state with a critical temperature of 3.2 K.

Contribution

It provides the first comprehensive bulk and microscopic evidence for a fully gapped, time-reversal symmetric superconducting state in LaOs$_{4}$As$_{12}$, clarifying previous conflicting findings.

Findings

Superconducting transition temperature $T_C$ = 3.2 K confirmed by heat capacity.

Superfluid density saturation indicates a fully gapped superconductivity.

No spontaneous magnetic field detected, preserving time-reversal symmetry.

Abstract

Filled skutterudite compounds have gained attention recently as an innovative platforms for studying intriguing low-temperature superconducting properties. Regarding the symmetry of the superconducting gap, contradicting findings from several experiments have been made for LaRu$_{4}$As$_{12}$ and its isoelectronic counterpart, LaOs$_{4}$As$_{12}$. In this vein, we report comprehensive bulk and microscopic results on LaOs$_{4}$As$_{12}$ utilizing specific heat analysis and muon-spin rotation/relaxation ($\mu$SR) measurements. Bulk superconductivity with $T_C$ = 3.2 K was confirmed by heat capacity. The superconducting ground state of the filled-skutterudite LaOs$_{4}$As$_{12}$ compound is found to have two key characteristics: superfluid density exhibits saturation type behavior at low temperature, which points to a fully gapped superconductivity with gap value of $2\Delta/k_BT_C$ = 3.26; additionally, the superconducting state does not show any sign of spontaneous magnetic field, supporting the preservation of time-reversal symmetry. These results open the door for the development of La-based skutterudites as special probes for examining the interplay of single- and multiband superconductivity in classical electron-phonon systems.