Shin-Ming Huang, Chung-Yu Mou
Based on an effective 12-orbital tight-binding model, we examine the
superconducting states induced by the antiferromagnetic fluctuations for
iron-vacancy-ordered A$_{y}$Fe$_{2-x}$Se$_{2}$. It is shown that due to the
broken reflection symmetry of the iron vacancies, new superconducting states
with $C_{4h}$ symmetry emerges. In particular, we show that the in the $C_{4h}$
symmetry, zeros of angles for the pairing momenta are free parameters. Hence
there are more degrees of freedoms to characterize the superconducting gaps,
which can further increase the gain of the condensation energy. Nonetheless,
similar to other iron-based superconductors, the singlet ground state is still
dominated by \textit{s}-wave or \textit{d}-wave, which are nearly degenerate
with anisotropic gaps. Furthermore, \textit{s}-wave and \textit{d}-wave
superconducting states are separated by a quantum critical point controlled by
the Hund's rule coupling $J_{H}$.
View original:
http://arxiv.org/abs/1202.1063
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