Pressure stability of superconductivity in Nb3Al: Role of low-frequency Nb–Nb chain vibrations and electron–phonon interplay

Abstract

Nb 3 Al , an A15-phase superconductor, exhibits exceptional stress–strain tolerance and high critical current density, making it a promising candidate for high-field magnet applications. Using first-principles calculations, we investigate the structural, electronic, phonon, and superconducting properties of Nb3Al under hydrostatic pressure (0–15 GPa). At ambient pressure, the calculated electron–phonon coupling strength λ≃1.71 and superconducting transition temperature TC≃19.1 K agree well with experiments. The high electronic density of states near the Fermi level, enhanced by Van Hove singularities, strengthens electron–phonon interactions and contributes to the elevated TC. Phonon spectral and linewidth analyses reveal that low-frequency modes associated with Nb–Nb chains dominate the electron–phonon coupling and are key to the superior superconducting performance of the A15 phase. Under pressure, λ decreases while the characteristic phonon energy ωlog increases; the resulting competition leads to a non-monotonic variation of TC. Remarkably, the total suppression of TC over the entire pressure range is less than 3%, demonstrating exceptional pressure stability. These findings highlight the crucial role of Nb–Nb chain vibrations and the delicate interplay between λ and ωlog in maintaining superconductivity under pressure, supporting Nb3Al as a promising alternative to Nb3Sn for high-field magnets, wherein it demonstrates exceptional pressure stability relative to Nb3Sn.