Superconductivity and copper valence in CuxBi2Se3

Min Nan Ou^1*, Shih-Hsun Yu^1,2,3, Tsu Lien Hung¹, Mitch M. C. Chou^2,3, Yang-Yuan Chen¹

¹Institute of Physics, Academia Sinica, Taipei City, Taiwan
²epartment of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan
³NSC Taiwan Consortium of Emergent Crystalline Materials (TCECM), Kaohsiung, Taiwan

* Presenter:Min Nan Ou, email:oumn@gate.sinica.edu.tw

The discovering of unconventional superconductivity by Ando et al. on copper intercalated Bi2Se3-based alloys1 revealed a candidate material for the realization of the MBS. However, understanding of the role of Cu atoms remains an issue on what the Cu contributing to the formation of superconducting quasiparticles. In this work, a series of CuxBi2Se3 (x= 0~ 0.3) crystals prepared with Bridgman method followed by an electrochemical technique (EC method) at room temperature. The analysis of powder x-ray diffraction, energy dispersive spectroscopy, x-ray photoelectron spectra Auger electron spectra, and electron energy loss spectroscopy imply and support that the zero-valence copper exists in between Bi2Se3 quintuple layers (QLs). The further study on temperature-dependent electrical resistance and magnetic susceptibility revealed a sharp superconducting transition at about TC = 3 ~ 3.5 K with a large shielding fraction of ~ 84%. On the optimized 10 at% of Cu, the analysis of specific heat capacity suggested that the superconducting volume fraction is around 53 ~ 80 %. The results of this work suggested that the formation of superconducting quasiparticles may not relate to the charge transfer of copper.

Keywords: superconductivity, topological insulator, single crystal, electrochemical intercalation