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There is considerable interest in uncovering the physics of iron-based superconductivity from the alkaline iron selenides, a materials class containing an insulating phase (245 phase) and a superconducting (SC) phase. Due to the microstructural complexity of these superconductors, the role of the 245 phase in the development of the superconductivity has been a puzzle. Here we demonstrate a comprehensive high-pressure study on the insulating samples with pure 245 phase and biphasic SC samples. We find that the insulating behavior can be completely suppressed by pressure in the insulating samples and also identify an intermediate metallic (M ) state. The Mott insulating (MI) state of the 245 phase and the M state coexist over a significant range of pressure up to ß10 GPa, the same pressure at which the superconductivity of the SC samples vanishes. Our results reveal the M state as a pathway that connects the insulating and SC phases of the alkaline iron selenides and indicate that the coexistence and interplay between the MI and M states is a necessary condition for superconductivity. Finally, we interpret the M state in terms of an orbital selectivity of the correlated 3d electrons.

On the basis of the excellent catalytic activity of NH2-Ni-MOF(c), a sensitive electrochemical aptasensor for CRP detection is first established.

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The discovery of new families, beyond graphene, of two-dimensional (2D) layered materials has always attracted great attention. However, it has been challenging to artificially develop layered materials with honeycomb atomic lattice structure composed of multicomponents such as hexagonal boron nitride. Here, through the dimensional manipulation of a crystal structure from sp3-hybridized 3D-ZnSb, we create an unprecedented layered structure of Zintl phase, which is constructed by the staking of sp2-hybridized honeycomb ZnSb layers. Using structural analysis combined with theoretical calculation, it is found that the 2D-ZnSb has a stable and robust layered structure. The bidimensional polymorphism is a previously unobserved phenomenon at ambient pressure in Zintl families and can be a common feature of transition metal pnictides. This dimensional manipulation of a crystal structure thus provides a rational design strategy to search for new 2D layered materials in various compounds, enabling unlimited expansion of 2D libraries and corresponding physical properties.

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