Enhanced Nernst effect by nematic fluctuations in an iron based superconductor

Nematic fluctuations are expected to enhance superconductivity in iron based superconductors which undergo a transition to nematic order. Motivated by recent Nernst effect measurements we investigate theoretically transport properties within a minimal electronic model consisting of two orbitals, with interactions that enhance nematic fluctuations. We apply a many-particle renormalization method to calculate current-current correlation functions and show that the correlation between currents in perpendicular directions are particularly enhanced by interactions between different orbitals. This property gives rise to a direct coupling of the Nernst effect to nematic fluctuations. We discuss our results in the context of recent Nernst effect experiments in BaFe${}_2$As${}_2$.