Model for the Magnetic Order and Pairing Channels in Fe Pnictide Superconductors

Abstract

A two-orbital model for Fe-pnictide superconductors is investigated using computational techniques on two-dimensional square clusters. The hopping amplitudes are derived from orbital overlap integrals, or by band structure fits, and the spin frustrating effect of the plaquette-diagonal Fe-Fe hopping is remarked. A spin striped state is stable in a broad range of couplings in the undoped regime, in agreement with neutron scattering. Adding two electrons to the undoped ground state of a small cluster, the dominant pairing operators are found. Depending on the parameters, two pairing operators were identified: they involve inter-xz-yz orbital combinations forming spin singlets or triplets, transforming according to the B2g and A2g representations of the D4h group, respectively.

Magnetic order in orbital models of the iron pnictides

“…The two-orbital model of Raghu et al 43 was one of the first attempts to model the pnictides from an orbital point of view, and also the first of a number of similar two-orbital models. 42,52,55,77 As it only keeps the xz and yz orbitals, it may be regarded as a minimal orbital model of the system. Although it is likely too simple to give quantitative agreement with experiment, it is nevertheless of interest to us as it qualitatively captures the variation of the orbital character about the Fermi surface and hence provides important clues to the ordering mechanism.…”

“…A large number of different orbital tightbinding models have therefore been proposed involving between two or five of the Fe 3d orbitals, 42,43,48,51,52,54,56,59,60,64,65,[77][78][79] or also including the As 4p orbitals 45,80 and even orbitals from outside the FeAs planes. 81 Although the existence of superconductivity in these models has been extensively studied, 40,[44][45][46]48,51,53,56,60,63,64,66 the magnetic behaviour remains rather poorly understood.…”

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.…”

Competition between superconductivity and nematic order: Anisotropy of superconducting coherence length

“…We will not address microscopic questions addressed in other literatures [16][17][18][19][20][21][22][23] , for example, role of orbital physics in nematic ordering 24 , but focus on general results on the interplay between the two orders that follow from the symmetries of the order parameter and the presence of a Fermi surface. We will show that the Fermi surface induces strong competition, which is especially important in the vortex core, and which can greatly enhance the anisotropy in the vortex shape.…”