Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article)

Abstract

Angle resolved photoemission spectroscopy (ARPES) reveals the features of the electronic structure of quasitwo-dimensional crystals, which are crucial for the formation of spin and charge ordering and determine the mechanisms of electron-electron interaction, including the superconducting pairing. The newly discovered ironbased superconductors (FeSC) promise interesting physics that stems, on one hand, from a coexistence of superconductivity and magnetism and, on the other hand, from complex multi-band electronic structure. In this review I want to give a simple introduction to the FeSC physics, and to advocate an opinion that all the complexity of FeSC properties is encapsulated in their electronic structure. For many compounds, this structure was determined in numerous ARPES experiments and agrees reasonably well with the results of band structure calculations. Nevertheless, the existing small differences may help to understand the mechanisms of the magnetic ordering and superconducting pairing in FeSC.

Multiple phase transitions in Pauli-limited iron-based superconductors

“…However, it should be had in mind that in many IBSC systems superconductivity can coexist with magnetic order. [45] In this paper, without specifying the mechanisms responsible for the forming of superconducting phases, we introduce a superconducting pairing between the quasi-particles in bands ε, which is a good approximation in the limit of weak or vanishing inter-band pairing [46]. Superconducting states with non-zero total momentum of Cooper pairs (TMCP) can be described by the phenomenological effective Hamiltonian:…”

Quasiparticle interference in multiband superconductors with strong coupling

“…On the other hand it may enhance orbital fluctuations, favoring s ++ superconductivity [19], with the order parameter having the same sign for the electron and the hole pockets. Therefore, such a sign change of the order parameter between the electron and hole pockets should hint at the possible pairing mechanism [16,[20][21][22][23][24][25].…”

Spin and Charge Susceptibilities of the Two-Orbital Model within the Cluster Perturbation Theory for Fe-Based Materials

“…2. The model can be used to describe the two electronic components scenario [31] where the bottom or the top of one of the bands is close to the chemical potential [18]. Similar scenario with the proximity to a Lifshitz transition has been proposed earlier for cuprates [32].…”

“…Agreement between the experimental FS and the one theoretically obtained within density functional theory (DFT) as well as the smallness of the magnetic moment in most FeBS and absence of Mott insulating state even in the undoped materials assert that the interaction is weak. On the other hand, comparison of ARPES (angle-resolved photoemission spectroscopy) results and DFT bands shows the bandwidth reduction about two to three times [18], and the redistribution of spectral wight from the Drude peak to higher energies in optical conductivity of LaFePO and BaFe 2 As 2 points out to the at least moderate electronic correlations [19]. While the use of hybrid methods like LDA+DMFT (local density approximation + dynamical mean-field theory) to treat electronic correlations allows to describe some physical properties of FeBS [20][21][22][23], nonlocal spin fluctuations are beyond these approaches.…”