Electronic nematicity above the structural and superconducting transition in BaFe(AsP)

BaFe(AsP)の構造及び超伝導転移点より高温におけるネマティック相

笠原 成*; Shi, H. J.*; 橋本 顕一郎*; 利根川 翔*; 水上 雄太*; 芝内 孝禎*; 杉本 邦久*; 福田 竜生  ; 寺嶋 孝仁*; Nevidomskyy, A. H.*; 松田 祐司*

Kasahara, Shigeru*; Shi, H. J.*; Hashimoto, Kenichiro*; Tonegawa, Sho*; Mizukami, Yuta*; Shibauchi, Takasada*; Sugimoto, Kunihisa*; Fukuda, Tatsuo; Terashima, Takahito*; Nevidomskyy, A. H.*; Matsuda, Yuji*

The electron nematicity, which break rotational symmetry of the crystal lattice, has been recently observed in high- superconductors. In iron-pnictides, it has been associated with the tetragonal-to-orthorhombic structural transition at , and the observations has been limited in the orthorhombic phase or in the tetragonal phase under uniaxial strain. In this investigation we provide magnetic torque measurements, a thermodynamic evidence which clearly shows the development of nematicity well above and the persistence in the nonmagnetic superconducting regime. Combined with synchrotron X-ray measurements, our results identify two distinct temperatures-one at , signifying a true nematic transition, and the other at (), which we show to be not a true phase transition, but rather what we refer to as a "meta-nematic transition", in analogy to the well-known metamagnetic transition in the theory of magnetism.