Superconducting dome and microstructure properties of Rb0.8Fe1.6+xSe2 superconductors

Abstract

High quality Rb0.8Fe1.6+xSe2 single crystals are grown by a one-step melting growth method. Superconductivity has been observed in all samples with x ≥ 0.05 and the maximum critical temperature (Tc) ≈ 32 K has been obtained in samples with 0.1 ≤ x ≤ 0.2 from electronic resistivity measurement. A superconducting dome in the electronic phase diagram of Tc as a function of Fe content has been observed for the first time in this AxFeySe2 (A = K, Rb) superconducting system. Two coexisting phases with structural modulation vectors of q1 = 1/5[3a* + b*] and q2 = 1/2[a* + b*] have been observed in all superconducting samples by TEM observations. Moreover, phase separation in the superconducting crystals, which can be recognized as micro-stripes in the a–b plane, are found to be highly dependent on the Fe content.