Interplay between nematicity and superconductivity in iron-based superconductors

The iron-based high-Tc superconductors exhibit several remarkable features, including the multi-orbital character and the ubiquity of the nematic phase. One consequence of the multi-orbital Fermi surface is that the spin-fluctuation mediated pairing interactions are sensitive to the orbital spectral weight at the Fermi surface, leading to several different possible gap structures, such as nodeless s±, nodal s±, and d-wave. Focused on the orbital order induced in the nematic phase, I will discuss how the nematic order can manipulate the properties of SC. Our calculation shows that not only T_c is enhanced, but more importantly, the gap structure becomes a mixture of nearly degenerate s and d-wave states by increasing the external strain. This mixture of s and d wave pairing channels has been recently found in the superconducting phase of the bulk FeSe, when SC occurs deeply insider the nematic phase.