Non-universal gap structure in iron-based high-Tc superconductors

Authors:
  • KHK. Hashimoto
    K. Hashimoto
  • MYM. Yamashita
    M. Yamashita
  • SKS. Kasahara
    S. Kasahara
  • YSY. Senshu
    Y. Senshu
  • NNN. Nakata
    N. Nakata
  • STS. Tonegawa
    S. Tonegawa
  • KIK. Ikada
    K. Ikada
  • ASA. Serafin
    A. Serafin
  • ACA. Carrington
    A. Carrington
  • TTT. Terashima
    T. Terashima
  • HIH. Ikeda
    H. Ikeda
  • TST. Shibauchi
    T. Shibauchi
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Abstract
Experimental insight into the origin of the interactions which drive high temperature superconductivity can be gained from the anisotropy of the energy gap. In the high-T_c Fe-pnictide superconductors most measurements to date indicate that the energy gap is finite at all points on the Fermi surface, in sharp contrast to high-T_c cuprates which have zeros (nodes) in the gap. Here we report magnetic penetration depth and thermal conductivity data for BaFe_2(As_{1-x}P_{x})_2 (T_c=30 K) which show unambiguously that this material has an energy gap with line nodes. This is distinctly different from the nodeless gap found for (Ba,K)Fe_2As_2 which has similar T_c, electronic structure, and phase diagram. Our results indicate that repulsive electronic interactions play an essential role for Fe-based high-T_c superconductivity but that uniquely there are quasi degenerate pairing states, with and without nodes, which have similar T_c.