Spectroscopic signature of anisotropic order parameter in Kagome lattice superconductor LaRh₃B₂

The physics of the Kagome metal LaRh$_3$B$_2$ along with its superconductivity below 2.6 K, unlike other popular Kagome metals, is not known to be significantly influenced by the electron correlations. While the indirect techniques to probe the bulk superconducting properties of LaRh$_3$B$_2$ indicate a conventional isotropic order parameter, we show that the direct spectroscopic determination of the superconducting energy gap reveals an anomalous suppression of Andreev reflection between LaRh$_3$B$_2$ and a normal metal. This observation hints to the presence of incomplete superconducting gap formation, at least along certain momentum directions, and consequent low-lying quasiparticle states. An analysis of multiple Andreev reflection spectra captured at different points on the surface of LaRh$_3$B$_2$ reveals a distribution of the superconducting energy gap which is consistent with an anisotropic superconducting order parameter.