Impact of nematicity on the relationship between antiferromagnetic fluctuations and superconductivity in FeSe0.91S0.09 under pressure

Abstract

The sulfur-substituted FeSe system, FeSe1−xSx, provides a versatile platform for studying the relationship among nematicity, antiferromagnetism, and superconductivity. Here, by nuclear magnetic resonance (NMR) and resistivity measurements up to 4.73 GPa on FeSe0.91S0.09, we established the pressure-(p-) temperature (T) phase diagram in which the nematic state is suppressed with pressure showing a nematic quantum phase transition (QPT) around p=0.5GPa, two superconductivity (SC) regions separated by the QPT appear, and antiferromagnetic (AFM) phase emerges above ∼3.3GPa. From the NMR results up to 2.1 GPa, AFM fluctuations are revealed to be characterized by the stripe-type wave vector which remains the same for the two SC regions. Furthermore, the electronic state is found to change in character from non-Fermi liquid to Fermi liquid around the nematic QPT and persists up to ∼2.1GPa. In addition, although the AFM fluctuations correlate with Tc in both SC states, demonstrating the importance of the AFM fluctuations for the appearance of SC in the system, we found that, when nematic order is absent, Tc is strongly correlated with the AFM fluctuations whereas Tc weakly depends on the AFM fluctuations when nematic order is present. Our findings on FeSe0.91S0.09 were shown to be applied to the whole FeSe1−xSx system and provide an insight into the relationship between AFM fluctuations and SC in Fe-based superconductors.

Relationship Between Nematicity, Antiferromagnetic Fluctuations, and Superconductivity in FeSe1−xSx Revealed by NMR

“…The three-dimensional T-p-x phase diagram of FeSe 1−x S x up to p = 8 GPa has been reported by Matsuura et al [35] in which the AFM ordered phase shifts to higher p with increasing x. A typical p-T phase is shown in Figure 2A for the case of x = 0.09 [37]. In this case, with increasing p, the nematic phase disappears around p ~0.5 GPa corresponding to a putative nematic QPT, and the AFM state appears above p ~3.5 GPa.…”

“…Such two different SC states under p were also reported in x = 0.11 [39] and 0.12 [41], which is more apparent under H [41]. The presence of a series of nematic quantum phase transitions in the x-p phase diagram [35] allows the study of the correlation between T c and AFM fluctuations in the presence and absence of the nematic order [37].…”

“…The nematic phase in the S-substituted FeSe system is also controlled by pressure application and an AFM state appears at higher p [35][36][37][38]. The three-dimensional T-p-x phase diagram of FeSe 1−x S x up to p = 8 GPa has been reported by Matsuura et al [35] in which the AFM ordered phase shifts to higher p with increasing x.…”

“…In this case, with increasing p, the nematic phase disappears around p ~0.5 GPa corresponding to a putative nematic QPT, and the AFM state appears above p ~3.5 GPa. In addition to the nematic, AFM, and SC states, Fermi liquid behaviors were reported at low temperatures in x = 0.09 (see Figure 2A) [37] and 0.11 [39] after the suppression of the nematic order by applying p. The Fermi liquid phase was recently attributed to the presence of a quantum griffiths phase close to the nematic QPT [40]. Similar to the T-x phase diagram of FeSe 1−x S x , SC phase was shown to have two different states (SC1 and SC2) separated by the nematic QPT as shown in Figure 2A.…”

Fragile pressure-induced magnetism in FeSe superconductors with a thickness reduction

“…In FeSe 1−x S x , the nematic phase is suppressed as sulfur content increases, and a nematic quantum critical point is observed without the presence of magnetism [45,50,53]. Meanwhile, the SDW phase in FeSe 1−x S x only appears when pressure is applied and its onset pressure shifts to a higher value as sulfur content increases [46,49,54]. Intriguingly, high-T c phases appear at both ends of the SDW dome, suggesting that the enhanced magnetic fluctuations may help to increase T c [46].…”