Cesium vacancy ordering in phase-separated $\mathrm{C}{\mathrm{s}}_x\mathrm{F}{\mathrm{e}}_{2-y}\mathrm{S}{\mathrm{e}}_2$

Journal Article · Mon Sep 14 00:00:00 EDT 2015 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.92.094505· OSTI ID:1337837

Taddei, Keith M. ^[1]; Sturza, M. ^[2]; Chung, Duck -Yung ^[3]; Cao, H. B. ^[4]; Claus, H. ^[3]; Kanatzidis, Mercouri G. ^[5]; Osborn, R. ^[3]; Rosenkranz, Stephen ^[3]; Chmaissem, Omar ^[1]

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1. Northern Illinois Univ., DeKalb, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
2. Argonne National Lab. (ANL), Argonne, IL (United States); Leibniz Institute for Solid State and Materials Research Dresden IFW, Dresden (Germany)
3. Argonne National Lab. (ANL), Argonne, IL (United States)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
5. Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)

By simultaneously displaying magnetism and superconductivity in a single phase, the iron based superconductors provide a model system for the study of magnetism’s role in superconductivity. The class of intercalated iron selenide superconductors is unique amongst these in having the additional property of phase separation and coexistence of two distinct phases - one majority phase with iron vacancy ordering and strong antiferromagnetism and the other a poorly understood minority microscopic phase with a contested structure. Adding to the intrigue, the majority phase has never been found to show superconductivity on its own while the minority phase has never been successfully synthesized separate from the majority phase. In order to better understand this minority phase, a series of high quality CsxFe2-ySe2 single crystals with (0.8 ≤ x ≤ 1; 0 ≤ y ≤ 0.3) were grown and studied. Neutron and x-ray powder diffraction performed on ground crystals show the average structure of the minority phase to be I4/mmm, however, the temperature evolution of its lattice parameters shows it to be distinct from the high temperature I4/mmm parent structure. Neutron and x-ray diffraction experiments performed on single crystal samples reveal the presence of previously unobserved discrete superlattice reflections that remove the degeneracy of the Cs sites in both the majority and minority phases and reduce their structural symmetries from body-centered to primitive. Group theoretical analysis in conjunction with structural modeling shows that the observed superlattice reflections originate from a three-dimensional Cs vacancy ordering in the minority phase. This model predicts a 25% vacancy of the Cs site which is consistent with the site’s refined occupancy. Magnetization measurements performed in tandem with neutron single crystal diffraction provide evidence that the minority phase is the host of superconductivity. Our results also reveal a superconducting dome in which the superconducting transition temperature varies as a function of the valence of iron.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
• Contributing Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Grant/Contract Number: AC05-00OR22725; AC02-06CH11357
• OSTI ID: 1337837
• Alternate ID(s): OSTI ID: 1215755; OSTI ID: 1356354
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 92, Issue 9; ISSN 1098-0121
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY