Multigap nodeless superconductivity in nickel chalcogenide TlNi2Se2

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi2Se2, a nickel chalcogenide heavy-electron superconductor with T-c similar or equal to 3.7 K. In zero field, the residual electronic contribution at T -> 0 K (kappa(0)/T) was well separated from the total thermal conductivity, which is less than 0.45% of its normal-state value. Such a tiny residual kappa(0)/T is unlikely contributed by the nodal quasiparticles. The nodeless gap structure is supported by the very weak field dependence of kappa(0)(H)/T in low magnetic fields. In the whole field range, kappa(0)(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.