Novel synthesis method of K$_{x}$Fe$_{2-y}$Se$_{2}$ single crystal

The discovery of superconductivity in K$_{x}$Fe$_{2-y}$Se$_{2}$ with $\sim $T$_{c}$ 31 K has triggered a great interest in the field of iron-based superconductors [1]. K$_{x}$Fe$_{2-y}$Se$_{2}$ superconductor has several practical advantages of relatively high $T_{c}$, high upper critical field (H$_{c2})$ and less toxicity compared to FeAs-based superconductors. However, the procedure for producing K$_{x}$Fe$_{2-y}$Se$_{2}$ single crystal is complicated and time-consuming: At first, the FeSe precursor was prepared, and then the single crystals of K$_{x}$Fe$_{2-y}$Se$_{2}$ were grown by the self-flux method. The simplification of the synthesis is really important for applications. We present a novel synthesis method of K$_{x}$Fe$_{2-y}$Se$_{2}$ single crystal, which is very simple and quick. A superconducting transition of this sample appeared at T $\sim $31.6 K. After quenching the sample, the calcurated volume fraction from dc magnetic susceptibility was dramatically increased, consistent with the previous report [2]. We will also report the details of the synthesis, transport properties and microstructures of the samples. 1)J.Guo, \textit{et al}, Phys. Rev. B \textbf{82}, 180520 (2010). 2)H. Lei, \textit{at el}, arXiv: 1109.0534.