L^.S pairing for the iron based superconductors

In this talk we propose L^.S pairing as a candidate superconducting state for the iron based superconductors within a three orbital model of t_2g electrons. This fully gapped state is spin-triplet (S = 1), orbital antisymmetric (L = 1), and has total angular momentum J = 0 (it is s-wave). The basic ingredients to stabilize this phase are strong Hund's interaction and sizable spin-orbit coupling. Crucially, details of the Fermi surface geometry are not important, by consequence the L^.S mechanism is universally applicable to all known pnictide and chalcogenide compounds. While early proposals for spin triplet pairing were dismissed due to the observation of clear Knight shift data, we show that the L^.S state does explain the Knight shift. Furthermore, the L^.S mechanism may be explored both within the weak coupling, itinerant and the strong coupling, atomistic pictures. It therefore has the potential to unify the success of both theoretical scenarios and is suitable for different compounds with dissimilar degree of correlations.