[PC8] Nickelates, Iron-based

4:00 PM - 4:15 PM JST(7:00 AM - 7:15 AM UTC)

[PC8-04] Elastoresistance study on electronic nematic behavior in iron-based superconductor Ba_1-xNa_xFe₂As₂

*Zifan Xu¹, Yoichi Kageyama², Asato Onishi¹, Kouseke Ishida³, Shigeyuki Ishida⁴, Hiroshi Eisaki⁴, Kota Ishihara¹, Kenichiro Hashimoto¹, Takasada Shibauchi¹ (1. Tokyo Univ. (Japan), 2. Kyoto Univ. (Japan), 3. Tohoku Univ. (Japan), 4. AIST (Japan))

Keywords:

Electronic nematicity,Rotational symmetry,Elastoresistance

The BaFe₂As₂-based iron superconductors represent a prototypical unconventional superconducting system, characterized by a rich interplay between magnetism, nematicity, and superconductivity. One of the most intriguing phenomena in these materials is the emergence of an electronic nematic phase, which arises from the spontaneous breaking of rotational symmetry while preserving translational invariance. This nematic phase often appears at low doping levels and is considered a precursor state to superconductivity. To investigate its nature, we performed elastoresistance measurements on the recently synthesized compound Ba_1-xNa_xFe₂As₂. This system has attracted considerable attention because, unlike most iron pnictides where nematic order is suppressed continuously with doping, it shows an unusual recovery of C₄ rotational symmetry at intermediate doping levels. This re-entrant C₄ phase is closely linked with a high-symmetry magnetic order, challenging the conventional view that nematicity and superconductivity are always directly coupled. By systematically tracking the nematic response across a wide range of Na concentrations, we reveal a complex doping evolution. Near the re-entrant C₄ phase, elastoresistivity coefficients display anomalous features, which may originate from Fermi surface reconstruction or competition between distinct magnetic orders. At even higher doping, a novel C₂' magnetic phase emerges, accompanied by vortex-like magnetic textures, further enriching the phase diagram. Curie-Weiss analysis of the nematic susceptibility shows that both the C₂ and C₂' phases exhibit similar nematic tendencies. Interestingly, a positive Curie-Weiss temperature persists even when long-range nematic order vanishes, implying the presence of nematic quantum criticality. These findings highlight the delicate balance of nematic, magnetic, and superconducting orders in Ba_1-xNa_xFe₂As₂ and provide new insights into the mechanisms of unconventional superconductivity.