1211.3944 (Youichi Yamakawa et al.)

Zigzag chain structure transition and orbital fluctuations in Ni-based
superconductors    [PDF]

Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani

We investigate the electronic state and structure transition of BaNi2As2, which shows a similar superconducting phase diagram as Fe-based superconductors. We construct the ten-orbital tight-binding model for BaNi2As2 by using the maximally localized Wannier function method. The Coulomb and quadrupole-quadrupole interactions are treated within the random-phase approximation. We find that the charge susceptibility of quadrupole O_{X2-Y2} has the largest peak structure at q = (pi, 0, pi) which is derived from both the in-plane and out-of-plane oscillations of Ni ions. We propose that the antiferro-quadrupole O_{X2-Y2} order with q = (pi, 0, pi) is the origin of the zigzag chain structure reported in experiments. The obtained antiferro-quadrupole fluctuations would then be the origin of the strong coupling superconductivity in Ni-based superconductors. We identify similarities and differences between Ni- and Fe-based superconductors.

View original: http://arxiv.org/abs/1211.3944