Substitution of Sc for Mg in MgB2: Effects on transition temperature and Kohn anomaly

Here we report the synthesis and characterization of Mg1−xScxB2 (0.12<x<0.27) system, with critical temperature in the range of 30 K >Tc >6 K. We find that the Sc doping moves the chemical potential through the 2-D/3-D electronic topological transition (ETT) in the s band where the “shape resonance” of interband pairing occurs. In the 3-D regime beyond the ETT we observe a hardening of the E2g Raman mode with a significant line-width narrowing due to the suppression of the Kohn anomaly over the range 0<q<2kF.