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

TL;DR

This study investigates the high-pressure electronic structure of niobium and Nb-Ti alloys, revealing Fermi surface topology changes and the persistence of Fermi liquid behavior, which are crucial for understanding their superconductivity.

Contribution

It provides the first detailed analysis of Fermi surface evolution in Nb and Nb-Ti alloys under ultra-high pressure, incorporating disorder and electronic correlations.

Findings

Significant Fermi surface topology changes at high pressure

Electronic correlations weaken with increasing pressure

Normal state remains a Fermi liquid with well-defined quasiparticles

Abstract

The electronic structure of pure niobium and the niobium-titanium alloy Nb$_{0.44}$Ti$_{0.56}$ in the bcc-phase at pressures up to $250$ GPa is investigated, to reveal possible factors conducing 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 Nb$_{0.44}$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 ultra high pressures allows notable insights into the nature of the electronic states near the Fermi level, i.e., within the energy scale relevant for superconducting pairing. Furthermore, our results clearly indicate the necessity of further experimental Fermi surface explorations.