Interplay of charge density wave and multiband superconductivity in 2H-Pd(x)TaSe(2)

2H-TaSe(2) has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at ≈122 K and a commensurate charge density wave (CCDW) state at ≈90 K, and superconductivity at T(C) ~ 0.14 K. Upon systematic intercalation of Pd ions into TaSe(2), we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x ~ 0.09–0.10. Moreover, T(C) shows a dramatic enhancement up to 3.3 K at x = 0.08, ~24 times of T(C) in 2H-TaSe(2), in proportional to the density of states N(E(F)). Investigations of upper critical fields H(c2) in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor γ(H) = [Image: see text], quasi-linear increase of [Image: see text], and an upward, positive-curvature in [Image: see text] near T(C). Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(E(F)) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of T(C) in Pd(x)TaSe(2).