Abstract
Intercalation of layered iron chalcogenide superconductors with guest species gives access to a gallery of layered phases with enhanced superconducting properties. While intercalation isolates the electronically active FeSe layers (cf. large interlayer separation, d), it also mediates the geometry and strength of electronic correlations within the basic building FeSe4 block, enquiring about its role in facilitating high Tc.
Here, the experimental platform Lix(C5H5N)yFe2-zSe2 is derived by intercalating [Li-C5H5N] adducts in the van der Waals gap of β-FeSe. Through low-temperature solvothermal techniques, two polytypes of Lix(C5H5N)yFe2-zSe2 with different d (~16.3 Å vs ~11.5 Å) and Tc (44 K vs 39 K) are made available, offering good testing ground to deliniate the conditions that foster high Tc¬ in such expanded lattice systems. Probing the systems with advanced experimental methods available at synchrotron x-ray and neutron facilities tells that intercalation acts as a tuning knob of both the atomic and electronic structure, mediating the materials' correlations across a wide range of length and time scales.
The outcomes highlight that intercalation-mediated carrier-doping and variations in the local geometry of the FeSe4 building blocks offer a means to optimize Tc at the frontier of large interlayer separation.