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

TL;DR

This study reports the growth of high-quality Rb0.8Fe1.6+xSe2 single crystals, revealing a superconducting dome as a function of Fe content, coexisting phases with specific modulations, and Fe-dependent microstructure phase separation.

Contribution

First observation of a superconducting dome in Rb0.8Fe1.6+xSe2, along with detailed microstructure and phase separation analysis using TEM.

Findings

Superconductivity appears for x > 0.05 with Tc up to 32 K.

A superconducting dome is identified as a function of Fe content.

Coexisting phases with specific modulation vectors are observed in all superconducting samples.

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 more than 0.05 and the maximum critical temperature Tc~32 K has been obtained in samples with x from 0.1 to 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 ab plane, are found to be highly dependent on the Fe content.