Tuning the charge density wave and superconductivity in Cu_x TaS₂

We report the characterization of layered 2H -type Cux TaS2 for 0≤x≤0.12. The charge density wave (CDW), at 70 K for TaS2, is destabilized with Cu doping. The sub-1 K superconducting transition in undoped 2H -TaS2 jumps quickly to 2.5 K at low x, increases to 4.5 K at the optimal composition Cu0.04 TaS2, and then decreases at higher x. The electronic contribution to the specific heat, first increasing and then decreasing as a function of Cu content, is 12 mJ mol-1 K-2 at Cu0.04 TaS2. Electron-diffraction studies show that the CDW remains present at the optimal superconducting composition but with both a changed q vector and decreased coherence length. We present an electronic phase diagram for the system.