Phonon anomaly and anisotropic superconducting gap in noncentrosymmetric Li₂(Pd_1-xPt_x)₃B

We report the systematic investigation of the specific heat of the noncentrosymmetric superconductor Li₂(Pd_1-xPt_x)₃B as a function of x. There is a large deviation of the phononic specific heat from the conventional Debye specific heat for Pt-rich samples. In contrast with the fully gapped conventional behavior for small x, a power-law temperature dependence of the electronic specific heat is observed even at x=0.5. These results manifest a strongly anisotropic or nodal superconducting gap even at x=0.5 and a nodal superconducting gap for x≳0.9.