1207.6571 (K. Okazaki et al.)

Evidence for cos(4\varphi) modulation of the superconducting-gap in
Fe(Te,Se)    [PDF]

K. Okazaki, Y. Ito, Y. Ota, Y. Kotani, T. Shimojima, T. Kiss, S. Watanabe, C. -T. Chen, S. Niitaka, T. Hanaguri, H. Takagi, A. Chainani, S. Shin

We study the superconducting(SC)-gap anisotropy of the \Gamma-centered hole Fermi surface in optimally doped FeTe_{0.6}Se_{0.4} (T_c = 14.5 K), using laser-excited angle-resolved photoemission spectroscopy (ARPES). We observe sharp superconducting coherence peaks at T = 2.5 K. In contrast to earlier ARPES studies but consistent with thermodynamic results, the momentum dependence shows a \cos(4\varphi) modulation of the SC-gap anisotropy. The observed SC-gap anisotropy strongly indicates that the pairing interaction is not a conventional phonon-mediated isotropic one. Instead, the results suggest the importance of second-nearest-neighbor electronic interactions between the iron sites in the framework of s_\pm-wave superconductivity.

View original: http://arxiv.org/abs/1207.6571