Gap symmetry of the noncentrosymmetric superconductor W3Al2C

A detailed zero-field and transverse-field muon spin relaxation/rotation ($\ensuremath{\mu}\mathrm{SR}$) experiments have been carried out on the recently discovered noncentrosymmetric superconductor ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ to speculate about its superconducting ground state. Bulk nature of superconductivity below 7.6 K is confirmed through magnetization and specific heat measurements. No change in the zero field $\ensuremath{\mu}\mathrm{SR}$ spectra collected above and below ${T}_c$ is visible, ruling out the possibility of spontaneous magnetic field below ${T}_c$. This confirms that time-reversal symmetry is preserved for ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ upon entering in the superconducting ground state. Temperature-dependent superfluid density [${\ensuremath{\rho}}_s(T)$], which directly reflects the superconducting gap symmetry is obtained by the analysis of spectra obtained from the transverse-field $\ensuremath{\mu}\mathrm{SR}$ experiments. Despite a noncentrosymmetric structure, ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ adopts a fully gapped spin-singlet superconducting ground state as confirmed through the analysis of ${\ensuremath{\rho}}_s(T)$ and ${C}_e(T)$. The zero-temperature value of gap is ${\mathrm{\ensuremath{\Delta}}}₀$ = 1.139(5) meV with gap-to-${T}_c$ ratio $2{\mathrm{\ensuremath{\Delta}}}₀/{k}_B{T}_c\ensuremath{\approx}3.48$, classifying this material as a weakly coupled superconductors. We have also revealed that the ratio ${T}_c/{\ensuremath{\lambda}}_{\mathrm{eff}}^{\ensuremath{-}2}$ is comparable to the class of unconventional superconductors, which points towards an unconventional pairing mechanism in ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$.