Sc substitution for Mg in MgB2: effects on Tc and Kohn anomaly

Here we report synthesis and characterization of Mg 1 − x Sc x B 2 (0.12 < x < 0.27) system, with critical temperature in the range of 30 > T c > 6 K. We find that the Sc doping moves the chemical potential through the 2D/3D electronic topological transition (ETT) in the σ band where the “shape resonance” of interband pairing occurs. In the 3D regime beyond the ETT we observe a hardening of the E 2 g Raman mode with a significant line-width narrowing due to suppression of the Kohn anomaly over the range 0 < q < 2k F