Superconductivity in a breathing kagome metals ROs₂ (R = Sc, Y, Lu)

We have successfully synthesized three osmium-based hexagonal Laves compounds ROs₂ (R = Sc, Y, Lu), and discussed their physical properties. LeBail refinement of pXRD data confirms that all compounds crystallize in the hexagonal centrosymmetric MgZn₂-type structure (P6₃ /mmc, No. 194). The refined lattice parameters are a = b = 5.1791(1) Å and c = 8.4841(2) Å for ScOs₂, a = b = 5.2571(3) Å and c = 8.6613(2) Å for LuOs₂ and a = b = 5.3067(6) Å and c = 8.7904(1) Å for YOs₂. ROs₂ Laves phases can be viewed as a stacking of kagome nets interleaved with triangular layers. Temperature-dependent magnetic susceptibility, resistivity and heat capacity measurements confirm bulk superconductivity at critical temperatures, T_c, of 5.36, 4.55, and 3.47 K for ScOs₂, YOs₂, and LuOs₂, respectively. We have shown that all investigated Laves compounds are weakly-coupled type-II superconductors. DFT calculations revealed that the band structure of ROs₂ is intricate due to multiple interacting d orbitals of Os and R. Nonetheless, the kagome-derived bands maintain their overall shape, and the Fermi level crosses a number of bands that originate from the kagome flat bands, broadened by interlayer interaction. As a result, ROs₂ can be classified as (breathing) kagome metal superconductors.