Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictide Superconductors

Abstract

We introduce and study an extended "t-U-J" two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the (π,0)-(0,π) spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A(1g) and B(2g) pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B(1g) states, suggesting that small changes in parameters may render any of the three channels stable.

Magnetic and pairing properties of a two-orbital model for the pnictide superconductors: a quantum Monte Carlo study

“…Since it is unrealistic to take the full quantum fluctuations into account in the usual theoretical methods, the important role of electronic correlations on the magnetism and superconductivity has not been thoroughly recognized. Despite the fact that there exist some unbiased numerical investigations of the two-orbital model, 6,14-16 these results are not sufficient enough to understand the electronic correlations in the two-dimensional systems because they are obtained either on a 8-site lattice 6,14,15 or on a diagonal ladder. 16 For a comprehensive and systematic understanding of the two-orbital model, 3,14 a quantum Monte Carlo (QMC) method is employed in this paper.…”

Spin fluctuations and pairing symmetry in AxFe2−ySe2: dual effect of the itinerant and the localized nature of electrons

“…Hence, we consider the effect of an admixture of both the on-site interactions and the J 2 exchange coupling here. A study based on the similar consideration for the interactions in the two-orbital model for pnictide superconductors with both electron and hole FS has been carried out from the strong coupling expansion 34 . We carry out the investigation using the FLEX approximation [35][36][37] , in which the Green's function and the spin/charge fluctuations are determined selfconsistently.…”

Charge stripes in the two-orbital Hubbard model for iron pnictides

“…3,4,8 While the superconductivity and (π, 0) magnetism have received most of the attention, recent experiments have revealed an even more complex behavior in pnictides. For example, inelastic neutron scattering (INS) experiments reported evidence for spin incommensurability (spin IC) in the superconducting state of the hole very overdoped pnictide KFe 2 As 2 .…”

“…2-7 Among the most robust results recently unveiled are (i) the existence of an intermediate Hubbard U coupling regime where the undoped state is simultaneously antiferromagnetic and metallic 6,7 as found in transport and neutron scattering experiments, 1 and (ii) the presence of superconducting tendencies upon charge doping mainly in the A 1g channel (extended s±, with nodes), [2][3][4]8 with the nodal pairing states B 1g and B 2g located close in energy. 3,4,8 While the superconductivity and (π, 0) magnetism have received most of the attention, recent experiments have revealed an even more complex behavior in pnictides.…”