Nodeless kagome superconductivity in LaRu3Si2

We report muon spin rotation ($\ensuremath{\mu}\mathrm{SR}$) experiments together with first-principles calculations on microscopic properties of superconductivity in the kagome superconductor ${\mathrm{LaRu}}_{3}{\mathrm{Si}}_{2}$ with ${T}_{\mathrm{c}}\phantom{\rule{4pt}{0ex}}\ensuremath{\simeq}$ 7K. Below ${T}_{\mathrm{c}}$, $\ensuremath{\mu}\mathrm{SR}$ reveals type-II superconductivity with a single s-wave gap, which is robust against hydrostatic pressure up to 2 GPa. We find that the calculated normal state band structure features a kagome flat band, and Dirac as well as van Hove points formed by the Ru-$d{z}^{2}$ orbitals near the Fermi level. We also find that electron-phonon coupling alone can only reproduce a small fraction of ${T}_{\mathrm{c}}$ from calculations, which suggests other factors in enhancing ${T}_{\mathrm{c}}$ such as the correlation effect from the kagome flat band, the van Hove point on the kagome lattice, and the high density of states from narrow kagome bands. Our experiments and calculations taken together point to nodeless moderate coupling kagome superconductivity in ${\mathrm{LaRu}}_{3}{\mathrm{Si}}_{2}$.