Sevda Avci

Growth and superconductivity of FeSex crystals

Iron selenide (FeSex) crystals with lateral dimensions up to millimeters were grown via a vapor self-transport method. The crystals consist of the dominant α-phase with trace amounts of β-phase as identified by powder x-ray diffraction. With four-probe resistance measurements, we obtained a zero resistance critical temperature of 7.5 K and a superconducting onset transition temperature of up to 11.8 K in zero magnetic field as well as an anisotropy of 1.5±0.1 for the critical field. Magnetization measurements on individual crystals reveal the coexistence of superconductivity and ferromagnetism.

Magnetically driven suppression of nematic order in an iron-based superconductor

A theory of superconductivity in the iron-based materials requires an understanding of the phase diagram of the normal state. In these compounds, superconductivity emerges when stripe spin density wave (SDW) order is suppressed by doping, pressure or atomic disorder. This magnetic order is often pre-empted by nematic order, whose origin is yet to be resolved. One scenario is that nematic order is driven by orbital ordering of the iron 3d electrons that triggers stripe SDW order. Another is that magnetic interactions produce a spin-nematic phase, which then induces orbital order. Here we report the observation by neutron powder diffraction of an additional fourfold-symmetric phase in Ba1-xNaxFe2As2 close to the suppression of SDW order, which is consistent with the predictions of magnetically driven models of nematic order.

Phase relations in K xFe 2-ySe 2 and the structure of superconducting K xFe 2Se 2 via high-resolution synchrotron diffraction

Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K

Magnetoelastic coupling in the phase diagram of Ba1-xK xFe2As2 as seen via neutron diffraction

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Coincident structural and magnetic order in BaFe2(As1-x Px)2 revealed by high-resolution neutron diffraction

Fe

Tetragonal magnetic phase in Ba 1 − x K x Fe 2 As 2 from x-ray and neutron diffraction

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Magnetoelastic Coupling in the Phase Diagram of Ba1-xKxFe2As2

Se

Tetragonal magnetic phase inBa1−xKxFe2As2from x-ray and neutron diffraction

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Phase relations in K{sub x}Fe{sub 2-y}Se{sub 2} and the structure of superconducting K{sub x}Fe{sub 2}Se{sub 2} via high-resolution synchrotron diffraction

powder and superconductors in the K

Phase relations in KxFe2−ySe2and the structure of superconducting KxFe2Se2via high-resolution synchrotron diffraction

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