Transport property of Cu-intercalated Bi$_2$Se$_3$

Cu$_x$Bi$_2$Se$_3$($T_{\mathrm{c}} \sim 3.8$ K)[1] is a promising candidate material to be a topological superconductor, and it is very important to clarify the origin of its superconductivity. However, Cu$_x$Bi$_2$Se$_3$ synthesized by Hor \textit{et al.} does not show zero resistivity below $T_{\mathrm{c}}$ [1], and some concerns still remain in the quality of samples. Recently, several groups reported the successful preparation of Cu-intercalated Bi$_2$Se$_3$ with zero resistivity by an electrochemical method [2] and the Bridgman method [3]. Here, we report transport properties of single crystals of Cu$_x$Bi$_2$Se$_3$ with zero resistivity prepared by the Bridgman method. We stress that the process of the quenching from a temperature of about 1000 K into cold water is of crucial importance in the crystal growth process. The grown crystal with $x=0.10$ shows zero resistivity at about 3.2 K. We also report the results of the intercalations of different metal elements [4].\\[4pt] [1] Y.~S. Hor \textit{et al.}, PRL 104 (2010) 057001.\\[0pt] [2] M. Kriener \textit{et al.}, PRL 106 (2011) 127004.\\[0pt] [3] T. Kirzhner \textit{et al.}, arXiv:1111.5805. T. V. Bay \textit{et al.}, arXiv:1112.0102.\\[0pt] [4] Y. Imai \textit{et al.}, J. Phys. Soc. Jpn. 81 (2012) 113708.