Elastoresistance study on iron-based superconductor Ba_1-xNa_xFe₂As₂

The electronic nematic state often appears in unconventional superconductors , and it is believed to be related to their superconducting mechanism.This state breaks rotational symmetry but keeps translational symmetry.

A representative system for studying the relationship between nematicity and superconductivity is the iron-based compound BaFe_₂As_₂, which belongs to the D₄h point group. When doped with sodium, the material exhibits both nematic behavior and superconductivity. Interestingly, at certain doping levels, the system recovers C₄ symmetry, accompanied by an unusual magnetic order. This phenomenon challenges the conventional view that nematicity is always associated with superconductivity.At higher doping levels, a new C₂′ phase appears, together with a vortex-like magnetic order. This study investigates the re-entrant behavior through elastoresistance measurements and characterizes the evolution of nematicity across different doping levels. .

The results show that near the re-entrant C4 phase, the elastoresistance coefficients exhibit two distinct anomalies, likely related to the accompanying magnetic order. Curie–Weiss fitting is used to analyze the evolution of the nematic phase, revealing that the C2 and C2′ phases possess similar nematic susceptibilities. At higher doping levels, signatures of quantum criticality are observed. For detailed experimental procedures, please refer to the presentation.