Extraordinary Doping Effects on Quasiparticle Scattering and Bandwidth in Iron-Based Superconductors

Abstract

The diversities in crystal structures and ways of doping result in extremely diversified phase diagrams for iron-based superconductors. With angle-resolved photoemission spectroscopy, we have systematically studied the effects of chemical substitution on the electronic structure of various series of iron-based superconductors. Beyond the Fermi-surface alteration that has been reported most often in the past, we found two more extraordinary effects of doping: (1) the site and band dependencies of quasiparticle scattering and, more importantly, (2) the ubiquitous and significant change of electronic correlation by both isovalent and heterovalent dopants in the iron-anion layer. Moreover, we found that the electronic correlation could be suppressed by applying either the chemical pressure or doping electrons but not by doping holes. Together with other findings provided here, these results complete the microscopic picture of the electronic effects of dopants, which facilitates a unified understanding of the diversified phase diagrams and resolutions to many open issues of various iron-based superconductors.

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Plain Language Summary

Replacing certain atoms in a material, a process known as chemical substitution or doping, can effectively tune a substance’s properties. For example, doping impurities into silicon started a revolution in the electronics industry in the 1940s; semiconductors now form the basis of modern transistors, light-emitting diodes, and CCD or CMOS photon detectors. We investigate the role of dopants in iron-based superconductors, which characteristically exhibit an unprecedentedly rich behavior against doping.

We focus on identifying the role of chemical substitution in iron-based superconductors and understanding what the dopants do and how they induce unconventional high-temperature superconductivity. We conduct a systematic investigation of the behavior of electrons in a variety of iron-based superconductors with angle-resolved photoemission spectroscopy, using experimental facilities in China, Japan, Switzerland, and the United States. We find that dopants modify the carrier density, introduce quasiparticle scattering, and vary the bandwidth in extraordinary ways. Our results show that bandwidth, which is closely related to electronic correlations, is likely the most universal electronic parameter to modulate superconductivity in iron-based superconductors; when the bandwidth is increased beyond a common range, superconductivity disappears.

The microscopic picture of doping effects that we have established facilitates a comprehensive and generic understanding of the rich and complex phase diagrams of various iron-based superconductors. Our results furthermore highlight future directions to search for new iron-based superconductors with higher superconducting transition temperatures.