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

Abstract

Crystalline FeSe is known to display strong nematic order below a weak tetragonal-orthorhombic structural transition around ${T}_{s}\sim 90$ K, and a superconducting transition at ${T}_{c}\sim 9\,{\rm{K}}$ . 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 ${s}_{\pm }$ 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.

Keywords

• superconductivity
• nematic order
• disorder effect