Superconducting properties of the C15-type Laves phase ZrIr2 with an Ir-based kagome lattice

Abstract

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr2. It crystallizes in a C15-type (cubic MgCu2-type, space group F d 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 ZrIr2 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 ZrIr2. ZrIr2 is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change ΔC e/γ T c ∼ 1.86 and the coupling strength Δ0/k B T c ∼ 1.92. First-principles calculations suggest that ZrIr2 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 SrIr2 and ThIr2, spin–orbit coupling has dramatic influences on the band structure in ZrIr2.