Effect of tunable spin-orbit coupling on the superconducting properties of LaRu3Si2 containing kagome-honeycomb layers

We report a detailed investigation of the superconducting properties of the kagome-honeycomb lattice compound LaRu3Si2 by systematically tuning the spin-orbit coupling (SOC) via doping of heavier elements Rh and Ir at the Ru site. All doped samples (for a doping level of 10 at. %) preserve the pristine hexagonal crystal structure in the space group P63/mmc, though a marginal lattice compression was noted for Rh doping. Based on the results of dc magnetization, resistivity, and heat capacity measurements, we derived the normal and superconducting state electronic and thermodynamic properties of the pristine and doped samples. Substitution of Ir/Rh at the Ru site of LaRu3Si2 resulted in a rather slow but linear suppression of superconducting transition temperature (Tc), which may be related to the decrease in the density of states. As manifested by the estimated electron-phonon (el-ph) coupling constant (lambda el-ph -0.58-0.66) and the normalized specific heat jump at Tc (AC/gamma Tc -1.5), the observed superconductivity in LaRu3Si2 and the doped variants is moderately coupled. We observed a nonmonotonous variation of the upper critical field [mu 0Hc2(0)] with respect to the doping concentration, as it is influenced by the effective SOC and the coherence length. Most strikingly, we found an enhancement of the superconducting gap parameter (40/kBTc) with doping concentration even though lambda el-ph remains essentially unchanged. Moreover, we also notice a nonzero residual electronic specific heat coefficient (gamma r) in the limit T -> 0 for all compositions. Interestingly, the evolution of the gamma r with the magnetic field can be well described by a root H dependence, which was attributed to multiband superconductivity.

Automated summary

We investigated the superconducting properties of the compound LaRu3Si2 on a kagome-honeycomb lattice by doping with heavier elements Rh and Ir. The doping resulted in a gradual suppression of superconducting transition temperature, although the observed superconductivity remained moderately coupled. The upper critical field showed a nonmonotonous variation with doping concentration, and the superconducting gap parameter was enhanced with doping concentration. We also observed a nonzero residual electronic specific heat coefficient for all compositions, indicating multiband superconductivity.