Schedule Sep 16, 2014
Are the hole Fermi surfaces missing in some of the Fe-based superconductors?
Kazuhiko Kuroki, Osaka Univ. & KITP

Fermi-surface-nesting originated spin fluctuation has been considered as a candidate forÂthe pairing glue in the iron-based superconductors. However, there have appeared some experimental observations that the hole Fermi surfaces are not present in some of the iron-based superconductors. For instance, in hydrogen doped 1111 materials, electron doping rate reaches up to 50 %, which in a rigid band picture would wipe out the hole Fermi surfaces, but still a very high Tc is attained. In K_xFe_2-ySe_2, the ARPES experiments show that the hole bands do not intersect the Fermi level. In the present talk, we will focus on these materials and show that the reduction of the nearest neighbor hopping within the d_xy orbital due to quantum interference tends to give rise to the d_xy hole Fermi surface. For the hydrogen doped 1111 systems, this explains the high Tc in the heavily doped regime. As for K_xFe_2-ySe_2, a very recent ARPES experiment that uses a high quality sample and tuned photon energy has revealed that there actually exists a hole band originating from the d_xy orbital that intersects the Fermi level. These results suggest the importance of the d_xy hole Fermi surface in the iron-based superconductors with high Tc, although the nesting itself is not as important as expected in the early days.

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