Enhancement of $T_c$ by disorder in FeSe

A recent electron irradiation experiment on FeSe single crystals has shown an unusual effect of disorder on superconductivity in this system. Point-like impurities introduced by electron irradiation increase $T_c$, while the structural transition temperature ($T_s$) gets suppressed. FeSe has strong nematic order below $T_s$, but there is no magnetic order, where one might expect $T_c$ enhancement by impurities. Here we examine the effect of disorder on the competition between nematicity and superconductivity. We find that the impurities can under some circumstances increase $T_c$, furthermore that show that the $T_c$ enhancement put constraints on the gap structure in FeSe.