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} (0.12T_{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}.Comment: 8 pages, 4 EPS figures, to be published in Phys. Rev.

Sc doping of MgB2: the structural and electronic properties of Mg1-xScxB2

We have investigated the effect of electron doping on the superconducting properties of MgB2. For the purpose we have synthesized several samples along the Mg1-xScxB2 section. The X-ray diffraction measurements reveal small changes in the lattice parameters suggesting that the Sc doping could be considered to simply fill the boron σ bands. Radiofrequency surface resistivity measurements has been used to obtain the variation of Tc with Sc doping. Increasing the Sc content, the exptl. Tc diverges from the Tc predicted by the BCS single band theory showing the key role of interchannel pairing near a shape resonance

Advances in doping MgB2: tuning the Fermi level to the "shape resonance" by Sc substitution

The authors synthesized superconducting Mg1-xScxB2 ternary system to explore the influence of electron doping on the electronic properties. An accurate characterization of several samples by x-ray diffraction and conductance measurements was performed. The Tc vanishes at the crit. concn. x at which the Fermi level is tuned to the top of the σ band. Sc doping in Mg1-xScxB2 allows one to tune the Fermi level to the shape resonance of the σ B superlattice with negligible changes of the lattice and the authors found a large Tc amplification by approaching the shape resonance as predicted by the authors' previous works