1209.5139 (M. Khodas et al.)

Vertical loop nodes in iron-based superconductors    [PDF]

M. Khodas, A. V. Chubukov

We consider Fe-based superconductors with $s^{+-}$ gap with accidental nodes on electron pockets. We analyze how the gap structure changes if we include into the consideration the hybridization between the two electron pockets (the inter-pocket hopping term with momentum $(\pi,\pi,\pi)$. We derive the hybridization term and relate it to the absence of inversion symmetry in the Fe-plane because of two non-equivalent locations of pnictogen (chalcogen) above and below the plane. We find that the hybridization tends to eliminate the nodes -- as it increases, the pairs of neighboring nodes approach each other, merge and disappear once the hybridization exceeds a certain threshold. The nodes disappear first around $k_z =\pi/2$, and vertical line nodes split into two vertical loops centered at $k_z =0$ and $k_z = \pi$. We also show that the hybridization moves the nodes along the loops away from the normal state Fermi surfaces. This creates a subset of $k-$points at which the peak in the spectral function does not shift as the system enters into a superconducting state ("no-shift" lines). These "no-shift" lines evolve with increasing hybridization in highly non-trivial manner and eventually form horizontal loops in $(k_x, k_y)$ plane, surrounding the nodes. Both vertical line nodes and horizontal "no-shift" loops surrounding them should be detectable in photoemission experiments.

View original: http://arxiv.org/abs/1209.5139