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

TL;DR

This study investigates how substituting scandium for magnesium in MgB2 affects its superconducting transition temperature and electronic properties, revealing a topological transition and suppression of the Kohn anomaly.

Contribution

It demonstrates the impact of Sc doping on the electronic structure and phonon modes in MgB2, highlighting the role of the electronic topological transition in superconductivity.

Findings

Critical temperature ranges from 6 to 30 K with Sc doping.

Sc doping induces a topological transition in the electronic structure.

Suppression of the Kohn anomaly observed in Raman spectra.

Abstract

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 sigma band where the ``shape resonance" of interband pairing occurs. In the 3D regime beyond the ETT we observe a hardening of the E_{2g} Raman mode with a significant line-width narrowing due to suppression of the Kohn anomaly over the range 0<q<2k_{F}.