Advanced first-principles theory of superconductivity including both lattice vibrations and spin fluctuations: The case of FeB4

J. Bekaert, A. Aperis, B. Partoens, P. M. Oppeneer, and M. V. Milošević
Phys. Rev. B 97, 014503 – Published 4 January 2018

Abstract

We present an advanced method to study spin fluctuations in superconductors quantitatively and entirely from first principles. This method can be generally applied to materials where electron-phonon coupling and spin fluctuations coexist. We employ it here to examine the recently synthesized superconductor iron tetraboride (FeB4) with experimental Tc2.4 K [H. Gou et al., Phys. Rev. Lett. 111, 157002 (2013)]. We prove that FeB4 is particularly prone to ferromagnetic spin fluctuations due to the presence of iron, resulting in a large Stoner interaction strength, I=1.5 eV, as calculated from first principles. The other important factor is its Fermi surface that consists of three separate sheets, among which two are nested ellipsoids. The resulting susceptibility has a ferromagnetic peak around q=0, from which we calculated the repulsive interaction between Cooper pair electrons using the random phase approximation. Subsequently, we combined the electron-phonon interaction calculated from first principles with the spin fluctuation interaction in fully anisotropic Eliashberg theory calculations. We show that the resulting superconducting gap spectrum is conventional, yet very strongly depleted due to coupling to the spin fluctuations. The critical temperature decreases from Tc=41 K, if they are not taken into account, to Tc=1.7 K, in good agreement with the experimental value.

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  • Received 7 October 2017
  • Revised 11 December 2017

DOI:https://doi.org/10.1103/PhysRevB.97.014503

©2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

J. Bekaert1,*, A. Aperis2,†, B. Partoens1, P. M. Oppeneer2, and M. V. Milošević1,‡

  • 1Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
  • 2Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden

  • *jonas.bekaert@uantwerpen.be
  • alex.aperis@physics.uu.se
  • milorad.milosevic@uantwerpen.be

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Issue

Vol. 97, Iss. 1 — 1 January 2018

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