Calculations of Spin Fluctuation Spectral Functions 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 extrapolations. In this work we present a method that combines density functional theory (DFT) in the local density approximation (LDA) with a momentum- and frequency-dependent pairing interaction derived from the Fluctuation Exchange (FLEX) type Random Phase Approximation (FLEX-RPA). This interaction is used to compute Eliashberg spectral functions α²F(ω) , which are central to spin fluctuation theory and offer new insights beyond previous treatments, specifically the confirmation of the usability of approximate BCS-like Tc equations. The overestimation of coupling constants shows that larger cutoff frequencies are necessary for Tc estimations. Further work is also required to explicitly exclude higher-order pairing symmetries and replicate the Tc dome.