“Measurement of a sign-changing two-gap superconducting phase in electron-doped Ba(Fe_{1-x}Co_x)_2As_2 single crystals using scanning tunneling spectroscopy” M. L. Teague, G. K. Drayna, G. P. Lockhart, P. Cheng, B. Shen, H.-H. Wen and N.-C. Yeh, Phys. Rev. Lett. 106, 087004 (2011). [arXiv:1007.5086]
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.087004