Maximizing by tuning nematicity and magnetism in FeSeS superconductors

Matsuura, Kohei*; Mizukami, Yuta*; Arai, Yuki*; Sugimura, Yuichi*; Maejima, Naoyuki*; Machida, Akihiko*; Watanuki, Tetsu*; Fukuda, Tatsuo  ; Yajima, Takeshi*; Hiroi, Zenji*; Yip, K. Y.*; Chan, Y. C.*; Niu, Q.*; Hosoi, Suguru*; Ishida, Kosuke*; Mukasa, Kiyotaka*; Kasahara, Shigeru*; Cheng, J.-G.*; Goh, S. K.*; Matsuda, Yuji*; Uwatoko, Yoshiya*; Shibauchi, Takasada*

A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature (). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving nonmagnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature () against pressure () and iso-valent S-substitution (), for FeSeS. By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended nonmagnetic tetragonal phase emerges, where shows a striking enhancement. The completed phase diagram uncovers that high- superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas remainslow near the nematic critical point.