Superconductivity in a new layered triangular-lattice system Li2IrSi2

We report on the crystal structure and superconducting properties of a novel iridium-silicide, namely Li2IrSi2. It has a Ag2NiO2-type structure (space group R-3m) with the lattice parameters a = 4.028 30(6) Å and c = 13.161 80(15) Å. The crystal structure comprises IrSi2 and double Li layers stacked alternately along the c-axis. The IrSi2 layer includes a two-dimensional Ir equilateral-triangular lattice. Electrical resistivity and static magnetic measurements revealed that Li2IrSi2 is a type-II superconductor with critical temperature (T c) of 3.3 K. We estimated the following superconducting parameters: lower critical field H c1(0) ∼ 42 Oe, upper critical field H c2(0) ∼ 1.7 kOe, penetration depth λ 0 ∼ 265 nm, coherence length ξ 0 ∼ 44 nm, and Ginzburg–Landau parameter κ GL ∼ 6.02. The specific-heat data suggested that superconductivity in Li2IrSi2 could be attributed to weak-coupling Cooper pairs.