Superconductivity at 1 K in Y-Au-Si quasicrystal approximants

We report the structural and physical properties of two Y-Au-Si (YAS) compounds, ${\mathrm{Y}}_{14.1}{\mathrm{Au}}_{69.2}{\mathrm{Si}}_{16.7}$ and ${\mathrm{Y}}_{15.4}{\mathrm{Au}}_{68.6}{\mathrm{Si}}_{16.1}$, which are 1/1 approximant crystals of a Tsai-type quasicrystal without intrinsic magnetic moments. The compounds differ by the presence of either a tetrahedron (Au,Si)${}_{4}$ or a single Y atom at the center of their characteristic structural building unit consisting of concentric polyhedral shells. Both compounds exhibit bulk superconductivity, which seems to be of a conventional type-II BCS type. The compound with Y atoms at the cluster center has a slightly higher transition temperature with a sharper step in the specific heat than the compound with tetrahedral units. We discuss the occurrence of this superconducting state in the light of the specific structural and physical properties of these quasicrystal approximants.