Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe_3-xSe_x

It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe₃. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe_3-xSe_x near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe_3-xSe_x single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ₀/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ₀/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe_3-xSe_x, which indicates conventional superconductivity despite of the existence of a CDW QCP.