Quasiparticle Fermi surfaces of niobium and niobium-titanium alloys at high pressure

The electronic structure of pure niobium and the niobium-titanium alloy ${\mathrm{Nb}}_0.44{\mathrm{Ti}}_0.56$ in the bcc phase at pressures up to $250\phantom{\rule{0.16em}{0ex}}\mathrm{G}\mathrm{Pa}$ is investigated, to reveal possible factors conducive toward the robust superconductivity reported for Ti-doped niobium upon a considerable volume reduction. We model the structural disorder using the coherent potential approximation, and the electronic correlations are taken into account using dynamical mean-field theory. At high pressure, a significant change in the topology of the Fermi surface is observed, while electronic correlations weaken with increasing pressure. Thus, the normal state of ${\mathrm{Nb}}_0.44{\mathrm{Ti}}_0.56$ is found to be a Fermi liquid with a well-defined Fermi surface and well-defined quasiparticles near it. The systematic study of the impact of disorder upon the Fermi surface at such ultrahigh pressures allows notable insights into the nature of the electronic states near the Fermi level. Furthermore, our results clearly indicate the necessity of further experimental Fermi surface explorations.