Superconducting properties of the C15-type Laves phase ZrIr ₂ with an Ir-based kagome lattice

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr ₂. It crystallizes in a C15-type (cubic MgCu ₂-type, space group $Fd\overline{3}m$ ) structure in which the Ir atoms form a kagome lattice, with cell parameters a = b = c = 7.3596(1) Å. Resistivity and magnetic susceptibility measurements indicate that ZrIr ₂ is a type-II superconductor with a transition temperature of 4.0 K. The estimated lower and upper critical fields are 12.8 mT and 4.78 T, respectively. Heat capacity measurements confirm the bulk superconductivity in ZrIr ₂. ZrIr ₂ is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change Δ C _e/ γ T _c ∼ 1.86 and the coupling strength Δ ₀/ k _B T _c ∼ 1.92. First-principles calculations suggest that ZrIr ₂ has three-dimensional Fermi surfaces with simple topologies, and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals. Similar to SrIr ₂ and ThIr ₂, spin–orbit coupling has dramatic influences on the band structure in ZrIr ₂.