Reversibly tuning the insulating and superconducting state in KxFe2-ySe2 crystals by post-annealing

Abstract

Since the discovery of superconductivity at 26 K in oxy-pnictide LaFeAsO1-xFx, enormous interests have been stimulated in the field of condensed matter physics and material sciences. Among the many kind of structures in the iron pnictide superconductors, FeSe with the PbO structure has received special attention since there is not poisonous pnictogen element in chemical composition and its structure is the simplest one. However, the superconducting transition temperature (Tc) in iron chalcogenide compounds is not enhanced as high as other iron pnictide superconductors under ambient pressure until the superconductivity at above 30 K in potassium intercalated iron selenide KxFe2-ySe2 was discovered. The insulating and the superconducting state are both observed in KxFe2-ySe2 with different stoichiometries and some groups have tuned the system from insulating to superconducting state by varying the ratio of starting materials[10, 11]. The recent data from neutron scattering suggest that the superconductivity may be built upon an ordered state of Fe vacancies as well as the antiferromagnetic state with a very strong ordered magnetic moment 3.4 B. Here we show that the superconductivity can actually be tuned on a single sample directly from an insulating state by post-annealing and fast quenching. Upon waiting for some days at room temperatures, the superconductivity will disappear and the resistivity exhibits an insulating behavior again. The spatial distribution of the compositions of the as-grown sample and the post-annealed-quenched one was analyzed by the Energy Dispersive X-ray Spectrum (EDXS) and found to be very close to each other. Therefore it is tempting to conclude that the superconductivity is achieved when the Fe-vacancies are in a random (disordered) state. Once they arrange in an ordered state by relaxation or slow cooling, the system turns out to be an insulator.

arXiv comment12 pages,5 figures

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Cited by in corpus (18)

• Phase relations in K_xFe_{2-y}Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction
• Influence of microstructure on superconductivity in K${}_x$Fe${}_{2-y}$Se${}_2$ and evidence for a new parent phase K${}_2$Fe${}_7$Se${}_8$
• Fe-vacancy order and superconductivity in PbO-type tetragonal β-Fe1-xSe
• Evolution of precipitate morphology during heat treatment and its implications for the superconductivity in KxFe1.6+ySe2 single crystals
• Effective doping and suppression of Fermi surface reconstruction via Fe vacancy disorder in KxFe2-ySe2
• Dependence of superconductivity in CuxBi2Se3 on quenching conditions
• Overview on the physics and materials of the new superconductor KxFe2-ySe2
• Strong and nonmonotonic temperature dependence of Hall coefficient in superconducting K${}_x$Fe${}_{2-y}$Se${}_2$ single crystals
• Spin reorientation in TlFe1.6Se2 with complete vacancy ordering
• Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation
• Temperature dependence of iron local magnetic moment in phase-separated superconducting chalcogenide
• Archimedean solid-like superconducting framework in phase-separated K0.8Fe1.6+xSe2 (0<=x<=0.15)
• Robust superconductivity and transport properties in (Li1-xFex)OHFeSe single crystals
• Evolution of superconductivity in isovalent Te-substituted KxFe2-ySe2 crystals
• Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides
• Superconductivity at the vacancy disorder boundary in K${}_x$Fe${}_{2-y}$Se${}_2$
• Annealing Effect on Microstructure and Superconductivity of KxFeySe2 Synthesized by an Easy One-step Method
• Multiband behavior and non-metallic low-temperature state of K${}_{0.50}$Na${}_{0.24}$Fe${}_{1.52}$Se${}_2$