About this Research Topic
In contrast to bulk iron selenide, which is a low-temperature superconductor, a single layer of iron selenide on a doped strontium-titanate substrate becomes a high-temperature superconductor, with a critical temperature in excess of 40 K. Photo-emission spectroscopy indicates that the substrate injects electrons into the iron-selenide layer that bury the hole bands at the center of the Brillouin zone below the Fermi level. An energy gap at the remaining electron Fermi-surface pockets at the corner of the Brillouin zone is also revealed in this way. The energy gap is confirmed by tunneling spectroscopy, while transport studies confirm the identification with a superconducting state. Strong electron doping of the iron-selenide layers can also be achieved by other means, such as by intercalation, by dosing with alkali atoms, and by the application of a gate voltage. The result, again, is high-temperature superconductivity, accompanied by the same Lifshitz transition of the Fermi surface topology.
The series of iron-pnictide compounds (Ba1-xKx)Fe2As2 shows high-temperature superconductivity when the electron Fermi-surface pockets are partially nested with hole Fermi-surface pockets at the center of the Brillouin zone. Evolution to the end-member compound KFe2As2 passes through a Lifshitz transition, where the electron bands at the corner of the Brillouin zone rise above the Fermi level. On the other hand, such strong hole doping results in low-temperature superconductivity.
We welcome contributions on the subject of iron-based superconductivity at strong electron or hole doping. A particular question of interest is the symmetry of the superconducting gap. For example, is it s-wave or d-wave? And if the former, how can that be reconciled with the absence of nested Fermi surfaces? Another question of interest has to do with the recent discovery of low-energy spin resonances about the Neel wave vector by inelastic neutron scattering in intercalated iron-selenide high-temperature superconductors. For example, does it point to competition between some type of magnetism and superconductivity? Lastly, recent scanning-tunneling microscopy (STM) of intercalated iron selenide found evidence for a Majorana zero mode in the quasi-particle spectrum of the vortex state. Is the zero-mode due to topological properties, or is it due to something else? We look forward to contributions on these topics, and on any other compelling topics related to strongly-doped iron-based superconductors. Both reports of original research and reviews of current the literature are welcome.
Keywords: iron pnictides, iron chalcogenides, iron selenide, pairing symmetries, electronic structure
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