Basic principles of disorder-induced electronic nematicity

Resolving the phenomenon of nematicity, i.e., the breaking of fourfold-rotational (C4) symmetry, remains an outstanding problem in the field of iron-based superconductors. A wide range of techniques have provided experimental evidence for electronic nematic behavior, while more recently, the nucleation of local nematicity around impurities has been also detected. While some of these results may be attributable to residual sample strain, the possible induction of local nematicity due to disorder appears as a prominent and, at the moment, a poorly-explored phenomenon. To shed light on this physics, we perform a detailed theoretical study of the role of disorder in systems exhibiting an electronic nematic instability, with an emphasis on temperatures above the critical temperature at which the spontaneous C4-symmetry breaking sets in. We employ both a phenomenological Ginzburg-Landau theory, as well as a microscopic model, and identify the spatial profile generated by a disorder configuration which either respects or explicitly breaks the fourfold rotational symmetry. In the former case, we find that while such a potential cannot induce net nematicity, it still modifies the Stoner criterion for the nematic instability, thus, generally enhancing the nematic critical temperature.