Abstract
The discovery in 2008 of the iron-based superconducting pnictide and chalcogenide compounds has provided an entirely new family of materials for studying the crucial interplay between superconductivity and magnetism in unconventional superconductors. The alkali-metal-intercalated iron selenide (AxFe2−ySe2, A = alkali metal) superconductors are of particular interest owing to their relatively high transition temperatures over 30 K and the co-existence of the superconducting state with antiferromagnetic ordering. Intrinsic phase separation on the mesoscopic scale is known to occur in ‘single crystals’ of these compounds, adding to the complexity of interpretation of bulk property measurements. In this study, we investigate the local electronic structure and chemistry of RbxFe2−ySe2 crystals using scanning microscopy techniques. Nano-focussed angle-resolved photoemission spectroscopy has enabled the band structure of the minority superconducting phase and the non-superconducting matrix to be measured independently and linked to the surface chemistry from the same regions using core level spectroscopy. Valence band mapping reveals the characteristic microstructure of these crystals, but does not have sufficient spatial resolution to enable the precise morphology of the superconducting phase to be elucidated. Cryogenic magnetic force microscopy has shown that the superconducting phase has a fine-scale stripey morphology that was not resolved in the scanning photoemission spectroscopy experiment. The correlation of these findings with previous microstructural studies, bulk measurements and first-principles density functional theory calculations paves the way for understanding the intriguing electronic and magnetic properties of these compounds.
Highlights
Since the discovery of iron-based superconductors in 2008 [1], a rich family of pnictide and chalcogenide compoundsSupercond
Cryogenic magnetic force microscopy has shown that the superconducting phase has a fine-scale stripey morphology that was not resolved in the scanning photoemission spectroscopy experiment
Angle-resolved photoemission spectroscopy (ARPES) studies have shown the absence of a hole pocket in the Fermi surface of the alkali metal doped iron chalcogenides [18,19,20], indicating that the nesting of hole and electron pockets, often considered to be of fundamental importance in iron-based superconductors, is not a prerequisite for superconductivity in these materials
Summary
Since the discovery of iron-based superconductors in 2008 [1], a rich family of pnictide and chalcogenide compoundsSupercond. The alkali metal doped iron chalcogenide superconductors, AxFe2−ySe2 (where A = K, Rb, Cs,Tl/K, Tl/Rb), have been a topic of great interest in recent years mainly as a result of their unusual magnetic behaviour combined with the ability to grow large, high quality single crystals which has enabled comprehensive exploration of the fundamental properties using a wide variety of diffraction and spectroscopic analysis techniques [12]. Angle-resolved photoemission spectroscopy (ARPES) studies have shown the absence of a hole pocket in the Fermi surface of the alkali metal doped iron chalcogenides [18,19,20], indicating that the nesting of hole and electron pockets, often considered to be of fundamental importance in iron-based superconductors, is not a prerequisite for superconductivity in these materials
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