S4Symmetric Microscopic Model for Iron-Based Superconductors

Abstract

Although iron-based superconductors are multiorbital systems with complicated band structures, we demonstrate that the low-energy physics which is responsible for their high-T c superconductivity is essentially governed by an effective two-orbital Hamiltonian near half filling. This underlying electronic structure is protected by the S 4 symmetry. With repulsive or strong next-nearest-neighbor antiferromagnetic exchange interactions, the model results in a robust A 1g s-wave pairing which can be mapped exactly to the d-wave pairing observed in cuprates. The classification of the superconducting (SC) states according to the S 4 symmetry leads to a natural prediction of the existence of two different phases, named the A and B phases. In the B phase, the superconducting order has an overall sign change along the c axis between the top and bottom As (or Se) planes in a single Fe-As (or Fe-Se) trilayer structure, the common building block of iron-based superconductors. The sign change is analogous to the sign change in the d-wave superconducting state of cuprates upon 90 rotation. Our derivation provides a unified understanding of iron pnictides and iron chalcogenides, and suggests that cuprates and iron-based superconductors share an identical high-T c superconducting mechanism.

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

“…[3][4][5] Regarding the minimal model capable of capturing the essential physics of pnictide SCs, some authors proposed more realistic threeand five-orbital models, 4,5 while others argued that the main physics of the pnictide SCs are contained in twoorbital models. 3,6,7 Because of their relative simplicity, as well as the fact that 6 the correct FS shape can be reproduced in both the doped and undoped cases, it is crucial to find out the properties of these two-orbital models.…”

Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO 3 films

“…In the iron-based superconductors, however, the parent compounds mostly exhibit a poor metallic behavior with an antiferromagnetic order, thus raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18), particularly whether the picture of doping a Mott insulator is relevant to the iron-based superconductors (1,3,11,16,17). Some theoretical calculations indicate that the iron-based superconductors may be in proximity to a Mott insulator (11,16,17), and attempts have also been made to unify cuprates and ironbased superconductors in theory (18). However, so far no clear experimental evidence of doping (or carrier concentration)-induced insulator-superconductor transition (or crossover) has been reported in the iron-based superconductors.…”

Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides

“…The two-orbital model was also shown to be suitable to describe the extended s-wave pairing believed to be relevant for ferropnictides, and other details of the superconducting phase. [31][32][33][34][35][36][37]66 In this work, we will study the doping and temperature effects on the electronic structure and spectral properties, using the following microscopic model for the normal state of pnictides:…”

“…30 is still recognized as a useful minimal model to describe the main features of the low-energy physics of ferropnictides. [31][32][33][34][35][36][37]41,42,66 Our paper is organized as follows. In Section II A we present the microscopic correlated two-orbital model adopted for our study of the normal state of Fe-based superconductors, and describe the analytical Green's function approach we used to calculate the electronic spectral density function and the total density of states including the correlations in second-order of perturbations ( further details of our analytical calculations appear in Supplementary Appendix A).…”