Nodeless superconductivity in a quasi-two-dimensional superconductor AuTe₂Se_4/3

We performed ultra-low temperature thermal conductivity measurements on the single crystal of a new gold-based quasi-two-dimensional superconductor AuTe₂Se_4/3, which has a superconducting transition temperature T_c=2.70 K. A negligible residual linear term κ₀/T in zero magnetic field is observed, which suggests fully gapped superconducting state. Furthermore, the field dependence of κ₀/T is similar to that of the multi-band s-wave superconductor BaFe_1.9Ni_0.1As₂ at low field. These results reveal multiple nodeless superconducting gaps in this interesting quasi-two-dimensional superconductor with Berezinsky-Kosterlitz-Thouless topological transition.