Superconductivity in TaSnS₂

The hexagonal TaSnS₂ sulphide is reported to be a superconductor with T_c = 2.8 K. However, its superconducting parameters have not been studied up to now. The powder of TaSnS₂ was compacted by spark plasma sintering (SPS). The measurements of magnetic susceptibility revealed a superconducting transition at T_c = 2.9 K in agreement with earlier report. The measurements of electrical resistivity and specific heat showed different critical magnetic fields μ₀H_c2 = 22 mT and 200 mT, respectively. This contradiction can indicate an anisotropy of superconducting properties caused by 2H-structure of TaSnS₂. The specific heat jump at the transition Δc_p/γT_c = 0.9 and the energy gap ratio Δ(0)/k_BT_c = 1.17 are well below the values (e.g. 1.43 and 1.76) predicted by BCS theory. This can be again due to an anisotropy of properties or/and by a multigap type of superconductivity. To finally shed light on the superconducting mechanisms in TaSnS₂ measurements on oriented crystals are required. High pressure measurements revealed that T_c for TaSnS₂ becomes zero for p > 2.5 GPa. The Raman measurements indicated a structural phase transition for TaSnS₂ above 7 GPa.