A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature (T c). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving non-magnetic 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 (T) against pressure (P) and isovalent S-substitution (x), for FeSe1−xSx. 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 non-magnetic tetragonal phase emerges, where T c shows a striking enhancement. The completed phase diagram uncovers that high-T c superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas T c remains low near the nematic critical point.

In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe 1−x S x superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near x ≈ 0.17, the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe 1−x S x as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.electronic nematicity | iron-based superconductors | nematic susceptibility | unconventional superconductivity | quantum critical point T he prime candidate for the unconventional mechanism of superconductivity in many strongly correlated electron systems including cuprate, iron-based, and heavy-fermion superconductors is based on magnetic fluctuations (1-4). In these materials, domeshaped superconducting phases appear in the vicinity of end point of the antiferromagnetic (AFM) order, where spin fluctuations are strongly enhanced. Recently, however, other competing or coexisting orders that break rotational symmetry of the system have been frequently found in these materials (5-8), and the importance of fluctuations of these orders on superconducting pairing has been suggested theoretically (9-12).In underdoped cuprate superconductors, unidirectional electronic correlations (stripe correlations) appear in the pseudogap state, whose relation with superconductivity is a center of debate. It has become more complicated after the charge density wave (CDW) order has been observed in a portion of this pseudogap region of the phase diagram (5). In iron pnictides, the tetragonal-toorthorhombic structural transition always precedes or coincides with the AFM transition (3). Below the structural transition temperature T s , electronic nematicity that represents a large electronic anisotropy breaking the C 4 rotational symmetry, is observed (7), which may have a similar aspect with the stripe correlations in underdoped cuprates. In both cases, however, the nematicity is largely coexisting and intertwined with other CDW and AFM orders. Large nematic fluctuations have been experimentally observed in BaFe 2 As 2 systems above T s , and these nematic fluctuati...

Electronic nematicity, a correlated state that spontaneously breaks rotational symmetry, is observed in several layered quantum materials. In contrast to their liquid-crystal counterparts, the nematic director cannot usually point in an arbitrary direction (XY nematics), but is locked by the crystal to discrete directions (Ising nematics), resulting in strongly anisotropic fluctuations above the transition. Here, we report on the observation of nearly isotropic XY-nematic fluctuations, via elastoresistance measurements, in hole-doped Ba1−xRbxFe2As2iron-based superconductors. While forx=0, the nematic director points along the in-plane diagonals of the tetragonal lattice, forx=1, it points along the horizontal and vertical axes. Remarkably, for intermediate doping, the susceptibilities of these two symmetry-irreducible nematic channels display comparable Curie–Weiss behavior, thus revealing a nearly XY-nematic state. This opens a route to assess this elusive electronic quantum liquid-crystalline state.

The interplay among magnetism, electronic nematicity, and superconductivity is the key issue in strongly correlated materials including iron-based, cuprate, and heavy-fermion superconductors. Magnetic fluctuations have been widely discussed as a pairing mechanism of unconventional superconductivity, but recent theory predicts that quantum fluctuations of nematic order may also promote high-temperature superconductivity. This has been studied in FeSe1−xSx superconductors exhibiting nonmagnetic nematic and pressure-induced antiferromagnetic orders, but its abrupt suppression of superconductivity at the nematic end point leaves the nematic-fluctuation driven superconductivity unconfirmed. Here we report on systematic studies of high-pressure phase diagrams up to 8 GPa in high-quality single crystals of FeSe1−xTex. When Te composition x(Te) becomes larger than 0.1, the high-pressure magnetic order disappears, whereas the pressure-induced superconducting dome near the nematic end point is continuously found up to x(Te) ≈ 0.5. In contrast to FeSe1−xSx, enhanced superconductivity in FeSe1−xTex does not correlate with magnetism but with the suppression of nematicity, highlighting the paramount role of nonmagnetic nematic fluctuations for high-temperature superconductivity in this system.

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Background and Aim The pathological features of non‐alcoholic steatohepatitis (NASH) have not been determined, so fundamental treatment has not been established. Adipose‐tissue‐derived stromal/stem cells (ADSCs) are beneficial for repair/regenerative therapy of impaired organs because of their immuno‐modulatory capability. In this study, we assessed how liver damage progresses during the early development phase of the murine NASH model and investigated whether ADSCs are preventatively efficacious against the fibrosis progression of NASH. Methods C57BL/6J mice were fed with atherogenic high fat or high‐fat diet 60 developing into NASH or simple steatosis. Their hepatic inflammatory cells (HICs) were analyzed by cDNA microarray. NASH mice were treated with ADSCs injected into spleen when hepatic inflammation was initially observed, and liver samples were analyzed. The effect of ADSCs on the mice hepatic stellate cell (HSC) line stimulated by recombinant IL‐17 and HICs from NASH mice was analyzed. Results The gene expression features of HICs implicated as humoral cytokine mediators of lymphoid cells during NASH development, compared with a simple steatosis model. One of the featured cytokines was IL‐17. The development of hepatic fibrosis was alleviated when NASH mice were treated with ADSCs as well as treated with anti‐IL‐17 antibody, and the frequency of IL‐17‐secreting HICs decreased. NASH‐HICs enhanced proliferation of HSCs, in which proliferation was sensitive to IL‐17 stimulation. The stimulatory effect of NASH‐HICs on the activation of HSCs was attenuated by co‐culture with ADSCs. Conclusion ADSCs treatment prevented progression of NASH fibrosis by suppressing IL‐17‐mediated inflammation, which was associated with HSCs activation.

Significance The notion of the quantum critical point (QCP) is at the core of modern condensed matter physics. Near a QCP of the symmetry-breaking order, associated quantum-mechanical fluctuations are intensified, which can lead to unconventional superconductivity. Indeed, dome-shaped superconducting phases are often observed near the magnetic QCPs, which supports the spin fluctuation–driven superconductivity. However, the fundamental question remains as to whether a nonmagnetic QCP of electronic nematic order characterized by spontaneous rotational symmetry breaking can promote superconductivity in real materials. Here, we provide an experimental demonstration that a pure nematic QCP exists near the center of a superconducting dome in nonmagnetic FeSe 1 − x Te x . This result evidences that nematic fluctuations enhanced around the nematic QCP can boost superconductivity.