Effect of disorder on the competition between nematic and superconducting order in FeSe

Crystalline FeSe is known to display strong nematic order below a weak tetragonal-orthorhombic structural transition around K, and a superconducting transition at . Recently, it was shown that electron irradiation, which creates pointlike potential scattering defects, has the surprising effect of enhancing T c while suppressing T s . Here we discuss a possible scenario for such an effect, which postulates a competition between superconductivity and nematic order. The transition to the nematic state is modeled by a mean field theory of a d-wave Pomeranchuk instability, together with a Cooper pairing interaction in both one- and multiband models. The effect of nonmagnetic impurities on both orders is treated on equal footing within the Born approximation. We find evidence that disorder can indeed enhance T c while suppressing the competing nematic order, but only in a multiband situation. We discuss our results in the context of experimental data on FeSe crystals.