Structure Of Iron-based Superconductors Research Articles

Orbital Selectivity in Electron Correlations and Superconducting Pairing of Iron-Based Superconductors

Electron correlations play a central role in iron-based superconductors. In these systems, multiple Fe 3d-orbitals are active in the low-energy physics, and they are not all degenerate. For these reasons, the role of orbital-selective correlations has been an active topic in the study of the iron-based systems. In this article, we survey the recent developments on the subject. For the normal state, we emphasize the orbital-selective Mott physics that has been extensively studied, especially in the iron chalcogenides, in the case of electron filling n∼6. In addition, the interplay between orbital selectivity and electronic nematicity is addressed. For the superconducting state, we summarize the initial ideas for orbital-selective pairing and discuss the recent explosive activities along this direction. We close with some perspectives on several emerging topics. These include the evolution of the orbital-selective correlations, magnetic and nematic orders, and superconductivity as the electron filling factor is reduced from 6 to 5, as well as the interplay between electron correlations and topological band structure in iron-based superconductors.

Effects of momentum-dependent quasiparticle renormalization on the gap structure of iron-based superconductors

We discuss the influence of momentum-dependent correlations on the superconducting gap structure in iron-based superconductors. Within the weak coupling approach including self-energy effects at the one-loop spin-fluctuation level, we construct a dimensionless pairing strength functional which includes the effects of quasiparticle renormalization. The stationary solution of this equation determines the gap function at $T_c$. The resulting equations represent the simplest generalization of spin fluctuation pairing theory to include the effects of an anisotropic quasiparticle weight. We obtain good agreement with experimentally observed anisotropic gap structures in LiFeAs, indicating that the inclusion of quasiparticle renormalization effects in the existing weak-coupling theories can account for the observed anomalies in the gap structure of Fe-based superconductors.

Phase separation in AyFe2-xSe2(A= K, Rb, Cs) superconductors

The interplay between superconductivity, magnetism and crystal structure in iron-based superconductors has attracted a great interest in the recent years as it is considered to be the key for understanding the mechanisms responsible for high temperature superconductivity. Alkali metal intercalated iron chalcogenide superconductors (A122) exhibit unique behavior which is not observed in other iron-based superconducting materials such as antiferromagnetic ordering above room temperature and iron vacancies ordering. These materials have complex crystal structures with several phase transitions and are mixtures of phases even in the form usually described as a single crystal. A pronounced reversible phase separation revealed in A122 single crystals, as well as controversies regarding the origin of superconductivity and the stoichiometry and symmetry of the superconducting phase are still in the forefront of scientific activity. Here we will present a diffraction study of the crystal structures, antiferromagnetic ordering and intrinsic phase separation in alkali-metal iron chalcogenides [1]. The complementary scanning electron microscope study, including high-resolution electron back-scatter diffraction mapping will be also presented [2].

铁基超导体掺杂和加压下结构对超导电性的影响 Influence of Structure on Superconductivity in Iron-Based Superconductors by Doping or under Pressure

根据铁基超导体晶体结构的不同分类，重点讨论了掺杂和加压下结构对超导电性的影响，总结了影响超导电性的局域结构因素及其理论和实践意义 According to the various classes of crystal structure of iron-based superconductors, the influence of structure on superconductivity is mainly discussed by doping or under pressure. The structural facts which influence the super- conductivity are summarized and the important significance in theory and practice is also discussed.

Effect of spin fluctuations on the electronic structure in iron-based superconductors

Magnetic inelastic neutron scattering studies of iron-based superconductors reveal a strongly temperature-dependent spin-fluctuation spectrum in the normal conducting state, which develops a prominent low-energy resonance feature when entering the superconducting state. Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS) allow us to study the fingerprints of fluctuation modes via their interactions with electronic quasiparticles. We calculate such fingerprints in 122 iron pnictides using an experimentally motivated spin-fluctuation spectrum and make a number of predictions that can be tested in ARPES and STS experiments. This includes discussions of the quasiparticle scattering rate and the superconducting order parameter. In quantitative agreement with experiment we reproduce the quasiparticle dispersions obtained from momentum distribution curves as well as energy distribution curves. We discuss the relevance of the coupling between spin fluctuations and electronic excitations for the superconducting mechanism.

Microstructural analysis of phase separation in iron chalcogenide superconductors

The interplay between superconductivity, magnetism and crystal structure in iron-based superconductors is a topic of great interest amongst the condensed matter physics community as it is thought to be the key to understanding the mechanisms responsible for high temperature superconductivity. Alkali metal doped iron chalcogenide superconductors exhibit several unique characteristics which are not found in other iron-based superconducting materials such as antiferromagnetic ordering at room temperature, the presence of ordered iron vacancies and high resistivity normal state properties. Detailed microstructural analysis is essential in order to understand the origin of these unusual properties. Here we have used a range of complementary scanning electron microscope based techniques, including high-resolution electron backscatter diffraction mapping, to assess local variations in composition and lattice parameter with high precision and sub-micron spatial resolution. Phase separation is observed in the CsxFe2−ySe2 crystals, with the minor phase distributed in a plate-like morphology throughout the crystal. Our results are consistent with superconductivity occurring only in the minority phase.