Abstract
The role of phase separation and the effect of Fe-vacancy ordering in the emergence of superconductivity in alkali metal doped iron selenides (A = K, Rb, Cs) is explored. High energy x-ray diffraction and Monte Carlo simulation were used to investigate the crystal structure of quenched superconducting (SC) and as-grown nonsuperconducting (NSC) single crystals. The coexistence of superlattice structures with the in-plane K-vacancy ordering and the Fe-vacancy ordering were observed in both the SC and NSC crystals alongside the I4/mmm Fe-vacancy-free phase. Moreover, in the SC crystals, an Fe-vacancy-disordered phase is additionally proposed to be present. Monte Carlo simulations suggest that it appears at the boundary between the I4/mmm vacancy-free phase and the I4/m vacancy-ordered phases (). The vacancy-disordered phase is nonmagnetic and is most likely the host of superconductivity.
- Received 17 May 2017
- Revised 25 April 2018
DOI:https://doi.org/10.1103/PhysRevB.97.184502
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