Calculations of spin fluctuation spectral functions α2F in high-temperature superconducting cuprates

Abstract

Spin fluctuations have been proposed as a key mechanism for mediating superconductivity, particularly in high-temperature superconducting cuprates, where conventional electron-phonon interactions alone cannot account for the observed critical temperatures. Traditionally, their role has been analyzed through tight-binding-based model Hamiltonians. In this work we present a method that combines density functional theory with a momentum- and frequency-dependent pairing interaction derived from the fluctuation exchange (FLEX) type random-phase approximation (FLEX-RPA) to compute Eliashberg spectral functions α2F(ω), which are central to the spin-fluctuation theory of superconductivity. We apply our numerical procedure to study a series of cuprates where our extracted material-specific α2F(ω) are found to exhibit remarkable similarities characterized by a sharp peak in the vicinity of 40–60 meV and their rapid decay at higher frequencies. Our exact diagonalization of a linearized BCS gap equation extracts superconducting energy-gap functions for realistic Fermi surfaces of the cuprates and predicts their symmetry to be dx2−y2 in all studied systems. Via a variation of onsite Coulomb repulsion U for the copper d electrons we show that the range of the experimental values of Tc can be reproduced in this approach but is extremely sensitive to the proximity of the spin-density wave instability. These data highlight challenges in building first-principle theories of high-temperature superconductivity but offer new insights beyond previous treatments, such as the confirmation of the usability of approximate BCS-like Tc equations, together with the evaluations of the material-specific coupling constant λ without reliance on tight-binding approximations of their electronic structures.

Source-reported materials — not catalogue approval

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