First-principles study of the robust superconducting state of NbTi alloys under ultrahigh pressures

Abstract

A recent experiment reported that robust superconductivity appears in NbTi alloys under ultrahigh pressures with an almost constant superconducting $T_c$ of ~19 K from 120 to 261.7 GPa [J. Guo et al., Adv. Mater. 31, 1807240 (2019)], which is very rare among the known superconductors. We investigate the origin of this novel superconducting behavior in NbTi alloys based on density functional theory and density functional perturbation theory calculations. Our results indicate that the pressure tends to transform NbTi alloys from a random phase to a uniformly ordered crystal phase, and the exotic robust superconductivity of NbTi alloys can still be understood in the framework of BCS theory. The Nb element in NbTi alloys plays a dominant role in the superconductivity at low pressure, while the NbTi crystal with an alternative and uniform Nb and Ti atomic arrangement may be responsible for the stable superconductivity under high pressures. The robust superconducting transition temperature of NbTi under ultrahigh pressure can be explained by a synergistic effect of the enhanced phonon frequency, the modestly reduced total electron-phonon coupling, and the pressure-dependent screened Coulomb repulsion.

arXiv comment7 pages, 5 figures, 1 table

References in corpus (13)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Phonons and related properties of extended systems from density-functional perturbation theory
• Conventional superconductivity at 203 K at high pressures
• Superconductivity at 250 K in lanthanum hydride under high pressures
• Electron-phonon interactions from first principles
• Evidence for superconductivity above 260 K in lanthanum superhydride at megabar pressures
• Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO
• EPW: A program for calculating the electron-phonon coupling using maximally localized Wannier functions
• Effect of Electron Count and Chemical Complexity in the Ta-Nb-Hf-Zr-Ti High-Entropy Alloy Superconductor
• High entropy alloy superconductors -- status, opportunities and challenges
• Isoelectronic Substitutions and Aluminium Alloying in the Ta-Nb-Hf-Zr-Ti High-Entropy Alloy Superconductor
• Pressure effects on the electronic structure and superconductivity of (TaNb)${}_{0.67}$(HfZrTi)${}_{0.33}$ high entropy alloy
• RSAVS superconductors: materials with a superconducting state that is robust against large volume shrinkage