We carried out a detailed study to investigate the existence of an insulating parent phase for FeSe superconductors. The insulating Fe₄Se₅ with √5 × √5 Fe-vacancy order shows a 3D-Mott variable-range-hopping behavior with a Verwey-like electronic correlation at around 45 K. The application of the RTA process at 450°C results in the destruction of Fe-vacancy order and induces more electron carriers by increasing the Fe³⁺ valence state. Superconductivity emerges with T_c ∼ 8 K without changing the chemical stoichiometry of the sample after the RTA process, resulting in the addition of extra carriers in favor of superconductivity.

中文翻译：

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铁空位排列的Fe4Se5：FeSe超导体的绝缘母相

我们进行了详细的研究，以研究FeSe超导体的绝缘母相的存在。具有√5×√5Fe空位顺序的绝缘Fe ₄ Se ₅表现出3D-Mott变程跳跃行为，在45 K左右具有类似Verwey的电子相关性。RTA工艺在450°C下的应用结果通过破坏Fe ³⁺价态，可以消除Fe的空位，并诱导更多的电子载流子。超导出现Ť_c〜8 K且在RTA处理后不改变样品的化学计量，导致添加了额外的有利于超导的载流子。