Competing d$_{xy}$ and s$_{\pm }$ Pairing Symmetries in Superconducting La$_{3}$Ni$_{2}$O$_{7}$ emerge from LDA+FLEX Calculations

Abstract

With recent discoveries of superconductivity in infinite--layer nickelates, and in La$_{3}$Ni$_{2}$O$_{7}$ under high pressure, new opportunities appeared that yet another family of high--temperature superconductors based on Ni element may exist in Nature as was previously the case of cuprates and iron based materials. With their famous strong Coulomb correlations among 3d electrons and the proximity to antiferromagnetic instability these systems represent a challenge for their theoretical description, and most previous studies of superconductivity relied on the solutions of simplified few--orbital model Hamiltonians. Here, on the other hand, we use a recently developed combination of density functional theory with momentum and frequency resolved self--energies deduced from the so--called Fluctuational--Exchange (FLEX)--type Random Phase Approximation (RPA) to study spin fluctuation mediated pairing tendencies in La$_{3}$Ni$_{2}$O$_{7}$ under pressure. This methodology uses first--principle electronic structures of an actual material and is free of tight--binding parametrizations employed in model Hamiltonian approach. Based on our numerical diagonalization of the BCS Gap equation we show that competing d$_{xy}$ and s$_{\pm }$ pairing symmetries emerge in superconducting La$_{3}$Ni$_{2}$O$% _{7}$ with the corresponding coupling constants becoming large in the proximity of spin density wave instability. The results presented here are discussed in light of numerous other calculations and provide on--going experimental efforts with predictions that will allow further tests of our understanding of unconventional superconductors.