Nodeless superconductivity in noncentrosymmetric LaRhSn

The superconducting order parameter of the noncentrosymmetric superconductor LaRhSn is investigated by means of low-temperature measurements of the specific heat, muon-spin relaxation/rotation $(\ensuremath{\mu}\mathrm{SR})$, and the tunnel-diode oscillator (TDO)-based method. The specific heat and magnetic penetration depth $[\ensuremath{\lambda}(T)]$ show an exponentially activated temperature dependence, demonstrating fully gapped superconductivity in LaRhSn. The temperature dependences of ${\ensuremath{\lambda}}^{\ensuremath{-}2}(T)$ deduced from the TDO-based method and $\ensuremath{\mu}\mathrm{SR}$ show nearly identical behavior, which can be well described by a single-gap $s$-wave model, with a zero-temperature gap value of $\mathrm{\ensuremath{\Delta}}(0)=1.77(4){k}_B{T}_c$. The zero-field $\ensuremath{\mu}\mathrm{SR}$ spectra do not show detectable changes upon cooling below ${T}_c$, and therefore there is no evidence for time-reversal-symmetry breaking in the superconducting state.