Superconductivity at the vacancy disorder boundary in K${}_x$Fe${}_{2-y}$Se${}_2$

Abstract

The role of phase separation in the emergence of superconductivity in alkali metal doped iron selenides A${}_x$Fe${}_{2-y}$Se${}_2$ (A = K, Rb, Cs) is revisited. High energy X-ray diffraction and Monte Carlo simulation were used to investigate the crystal structure of quenched superconducting (SC) and as-grown non-superconducting (NSC) K${}_x$Fe${}_{2-y}$Se${}_2$ single crystals. The coexistence of superlattice structures with the in-plane $\sqrt{2}\times \sqrt{2}$ K-vacancy ordering and the $\sqrt{5}\times \sqrt{5}$ Fe-vacancy ordering were observed in SC and NSC crystals along side the \textit{I4/mmm} Fe-vacancy free phase. Moreover, in the SC crystal an Fe-vacancy disordered phase is additionally present. It appears at the boundary between the \textit{I4/mmm} vacancy free phase and the \textit{I4/m} vacancy ordered phase ($\sqrt{5}\times \sqrt{5}$). The vacancy disordered phase is most likely the host of superconductivity.

5 pages, 3 figures, 2 tables

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Cited by in corpus (5)

• Fermi-Bose mixtures and BCS-BEC crossover in high-Tc superconductors
• Is there any hidden symmetry in the stripe structure of perovskite high temperature superconductors?
• Correlated disorder to order crossover in the local structure of K${}_x$Fe${}_{2-y}$Se${}_{2-z}$S${}_z$
• Multiple electronic components and Lifshitz transitions by oxygen wires formation in layered cuprates and nickelates
• Role of the Extra-Fe in K2-xFe4+ySe5 superconductors