Impacts of Co-doping on the superconductivity and the orbital ordering state in Fe$_{1-x}$Co$_x$Se single crystal studied by the electrical transport.

In the FeSe with the simplest crystal structure in the Fe-based superconductor families, although both the superconductivity and the orbital ordering states are investigated, the relation between them is still unclear[1-4]. Here, we report Co doping effects on the superconductivity and the orbital ordering state in Fe$_{1-x}$Co$_x$Se single crystals. The electrical transport measurements demonstrated that the superconductivity vanishes at 4$\%$ Co doping while the orbital ordering state may be robust against Co doping. Present results suggest that the orbital ordering state is not related to the emergence of the superconductivity in FeSe. [1] F. C. Hsu et al., Proc. Nat. Aca. Sci. 105, 14262 (2008). [2] K. Nakayama et al., arXiv:1404.0857v1 [3] T. Shimojima et al., Phys. Rev. B 90, 121111(R) (2014). [4] K. K. Huynh et al., Phys. Rev. B 90, 144516 (2014).