A combined method for synthesis of superconducting Cu doped Bi(2)Se(3)

We present a two-step technique for the synthesis of superconducting Cu(x)Bi(2)Se(3). Cu(0.15)Bi(2)Se(3) single crystals were synthesized using the melt-growth method. Although these samples are non-superconducting, they can be employed to generate high quality superconducting samples if used as precursors in the following electrochemical synthesis step. Samples made from Cu(0.15)Bi(2)Se(3) reliably exhibit zero-resistance even under the non-optimal quenching condition, while samples made from pristine Bi(2)Se(3) require fine tuning of the quenching conditions to achieve similar performance. Moreover, under the optimal quenching condition, the average superconducting shielding fraction was still lower in the samples made from pristine Bi(2)Se(3) than in the samples made from Cu(0.15)Bi(2)Se(3). These results suggest that the pre-doped Cu atoms facilitate the formation of a superconducting percolation network. We also discuss the useful clues that we gathered about the locations of Cu dopants that are responsible for superconductivity.