T. Tzen Ong, Piers Coleman
Motivated by the fully gapped superconductivity in iron-based superconductors with uncompensated electron pockets, we propose a spin-singlet analogue of the superfluid phase of ${}^3$He-B. We show that the staggered tetrahedral structure of these systems with 2 iron-atoms per unit cell introduces additional site and orbital band indices $\tau$ and $\alpha$ which act as internal isospin degrees of freedom, opening up a new class of tetrahedral and orbital ("TAO") triplet condensates. This permits two locally d-wave pairings to combine in quadrature without breaking lattice or time reversal symmetry, to produce a fully gapped topological superconductor. The internal chirality of this state is selected by a Josephson coupling between the d-wave components. This state is predicted to give rise to Raman-active excitations associated with the reversal of the gap chirality.
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http://arxiv.org/abs/1303.6325
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