Chemical enhancement of superconductivity in LaRu3Si2 with mode-selective coupling between kagome phonons and flat bands

In kagome metals, flat electronic bands induced by frustrated hopping are a platform for strong electron correlations. Here, we investigate the superconductivity in the kagome system LaRu3(Si1-xGex)2 by chemical pressure tuning while preserving the Ru-4d states that constitute the kagome flat bands. We observe a sizable enhancement in the density of states up to x=0.07, as determined by the specific heat, with a concomitant increase in the superconducting transition temperature Tc. Ge dopants induce a uniaxial lattice expansion along the c axis. Our first-principles calculations suggest that this mitigates the detrimental effect of hybridization between kagome layers and reduces the dispersion of the Ru-dx2-y2 flat band. The calculated chemical potential moves closer to the maximum in the energy-dependent density of states. Our result is consistent with a theoretical prediction of tunable flat-band superconductivity in LaRu3Si2 by mode-selective coupling between specific kagome phonons and the Ru-dx2-y2 orbitals.