Real structure influence on the electron–phonon coupling properties of niobium

Abstract

We performed density functional theory calculations using niobium (Nb) as a model system of a conventional superconductor, to correlate the distortion of twin defects with the electron–phonon coupling properties. Calculations using different settings of the Nb elementary cell (relaxed, distorted, super cell with zig‐zag twin defect) showed that only by including real structure elements into the setting, the Eliashberg spectral function representing the electron–phonon coupling properties was derived convincingly. Based on these density functional theory calculations of the electron–phonon cou‐ pling properties of Nb, we suggest a model for a combined superconducting/charge density wave ground state which uses a lattice distortion induced into the crystal by two‐dimensional defects as modulated background potential of the charge density wave phase. The coexistence of both phases is hereby necessary for a fine‐tuning of the Fermi surface within the small local domain of the defect to match the wavelength of the lattice distortion and the Fermi wavelength by pairing fermions to bosons. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)