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 Ts 90 K, and a superconducting transition at Tc 9 K. Recently, it was shown that electron irradiation, which creates pointlike potential scattering defects, has the surprising effect of enhancing Tc while suppressing Ts. Here we discuss a possible scenario for such an effect, which postulates a competition between s± 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 Tc while suppressing the competing nematic order, but only in a multiband situation.Wediscuss our results in the context of experimental data on FeSe crystals.