Electronic structure and phonon properties in the kagome metals RT3B2 (R = Y, Lu; T = Co, Os)

The RT3B2 (R = Y, Lu, T = Co, Os) family hosts a perfect kagome lattice of T atoms, offering an interesting platform to investigate the interplay of electronic structure, superconductivity, and lattice dynamics. Here, we compare two members of this family, LuOs3B2 and YCo3B2, with similar crystallography but differing chemical composition, which results in different electronic structures and correlation signatures, as well as distinct spinorbit coupling effects. We confirm superconductivity in LuOs3B2 with Tc = 4.75 K, while YCo3B2 remains nonsuperconducting above 1.8 K. Both materials exhibit kagome-derived electronic features, including quasiflat bands, Dirac cones, and van Hove singularities. Fermi surface calculations reveal a highly anisotropic electronic structure in YCo3B2, establishing a kz-selective metallic behavior and leading to strongly suppressed in-plane conduction, in contrast to the more isotropic fermiology of LuOs3B2. Phonon calculations for LuOs3B2 show imaginary modes, indicating potential lattice instabilities. Experimental estimates of the Wilson and KadowakiWoods ratios point to significant electronic correlations in both compounds.