Emergence of superconductivity in strongly correlated hole-dominated Fe1-xSe

Unusual Normal and Superconducting State Properties Observed in Hydrothermal Fe1-δ Se Flakes

“…Therefore, our results suggest that the emergent high-mobility electron pocket in the nematic FeSe does not favor the superconductivity. This is in agreement with our recent re-sults obtained in isovalently substituted [6] and irondeficient [10] FeSe single crystals. In addition, compared to the anisotropic upper critical field 𝐻 c2 (0) of CVT FeSe, [11−15] 𝐻 c2 (0) of the present hydrothermal Fe 1−𝛿 Se is found not only to be isotropic but also to reach a higher value of ∼42 T, which breaks the BCS Pauli limit [𝐻 BCS P (0) = 1.84𝑇 c ] by a factor of 1.8.…”

“…2(d)], indicating a persistent hole-dominant nature. This behavior of 𝑅 H (𝑇 ) for Fe 1−𝛿 Se turns out to be intermediate between those for stoichiometric CVT FeSe [7−9] and hydrothermal Fe 1−𝑥 Se with a small iron-vacancy amount 𝑥, [10] consistent with that 𝛿 is closer to 0. Therefore, the normal-state electronic properties of our hydrothermal Fe 1−𝛿 Se are distinctly different from those of CVT FeSe.…”

“…1 The cell parameter 𝑐 (with some uncertainty only in the third decimal), the pristine SAED pattern, and the 𝑇 c value all point to a small non-stoichiometry (with 𝛿 closer to 0) for the hydrothermal Fe 1−𝛿 Se, when comparing with the previous results. [10,19] port properties observed in our hydrothermal Fe 1−𝛿 Se, with emphasis on their significance in comparison with those seen in nematically ordered CVT FeSe. It is well known that an obvious kink at the structural 𝑇 s ∼ 90 K, as well as a metallic behavior in a wide temperature range, is a characteristic of the temperaturedependent resistivity of the nematic FeSe.…”

Magnetic-Field-Induced Spin Nematicity in FeSe1 – x S x and FeSe1 – y Te y Superconductor Systems

“…[45] Additionally, in prototypical Fe 1−𝑥 Se and intercalated (Li,Fe)OHFe 1−𝑥 Se compounds, 𝑇 c has been reported as being suppressed with the increased hole doping that is associated with the Fe-deficiency 𝑥, due to the hole-doping 𝑥 enhanced electronic correlations. [46,47] Therefore, further investigations are required to clarify the complex effects of electronic correlations on the superconductivity in multi-orbital/band iron-based compounds. Nevertheless, here an anti-correlation between 𝑇 c of the superconductivity and 𝑇 sn of the induced spin nematicity is observed in both FeSe 1−𝑥 S 𝑥 and FeSe 1−𝑦 Te 𝑦 samples (Fig.…”