Multigap nodeless superconductivity in nickel chalcogenide TlNi2 Se2

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi2Se2, a nickel chalcogenide heavy-electron superconductor with Tc≃3.7 K. In zero field, the residual electronic contribution at T→0 K (κ0/T) was well separated from the total thermal conductivity, which is less than 0.45% of its normal-state value. Such a tiny residual κ0/T is unlikely contributed by the nodal quasiparticles. The nodeless gap structure is supported by the very weak field dependence of κ0(H)/T in low magnetic fields. In the whole field range, κ0(H)/T exhibits an S-shaped curve, as in the case of nickel pnictides BaNi2As2 and SrNi2P2. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps.