Superconductivity in a new layered triangular-lattice system Li2IrSi2

We report on the crystal structure and superconducting properties of a novel iridium-silicide, namely Li 2 IrSi 2 . It has a Ag 2 NiO 2 -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 IrSi 2 and double Li layers stacked alternately along the c -axis. The IrSi 2 layer includes a two-dimensional Ir equilateral-triangular lattice. Electrical resistivity and static magnetic measurements revealed that Li 2 IrSi 2 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 Li 2 IrSi 2 could be attributed to weak-coupling Cooper pairs.