Correlation-enhanced odd-parity inter-orbital singlet pairing in LiFeAs

The rich variety of iron-based superconductors and their complex electronic structure lead to a wide range of possibilities for gap symmetry and pairing components. We solved, in the two-Fe Brillouin zone, the full frequency-dependent linearized Eliashberg equations to investigate spin-fluctuations mediated Cooper pairing for LiFeAs . The magnetic excitations were calculated with the random phase approximation on a correlated electronic structure obtained with density functional theory and dynamical mean field theory. The interaction between electrons through Hund's coupling promotes both the intra-orbital $d_{xz(yz)}$ and the inter-orbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional $s^{+-}$, acquires sizeable inter-orbital $d_{xy}-d_{xz(yz)}$ singlet pairing with odd parity under glide-plane symmetry. The combination of intra- and inter-orbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces [1]. We also explain the difference in pairing symmetry between LiFeAs and LiFeP [2]. \newline [1] R.~Nourafkan, G.~Kotliar, and A.-M.S.~Tremblay, Phys. Rev. Lett. \textbf{117}, 137001 (2016). [2] R.~Nourafkan, Phys. Rev. B \textbf{93}, 241116(R) (2016)