Maximizing Tc by tuning nematicity and magnetism in FeSe1-xSx superconductors

Abstract

A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature ($T_{\mathrm{c}}$). 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 overlap with each other, the effects of two orders on superconductivity remain perplexing. Here we construct the three-dimensional electronic phase diagram, temperature ($T$) against pressure ($P$) and isovalent S-substitution ($x$), for FeSe${}_{1-x}$S${}_x$, in which we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended nonmagnetic tetragonal phase emerges, where we find a striking enhancement of $T_{\mathrm{c}}$. The completed phase diagram uncovers two superconducting domes with similarly high $T_{\mathrm{c}}$ on both ends of the dome-shaped antiferromagnetic phase. The $T_{\mathrm{c}}(P,x)$ variation implies that nematic fluctuations unless accompanying magnetism are not relevant for high-$T_{\mathrm{c}}$ superconductivity in this system.

8 pages, 9 figures. A revised version will appear in Nature Communications