We report the low-temperature electronic and magnetic properties of the alkali metal-organic solvent intercalated iron selenide superconductor $\mathrm{Li}({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}{)}_{0.2}{\mathrm{Fe}}_2{\mathrm{Se}}_2$ using muon-spin-spectroscopy measurements. The zero-field muon spin relaxation ($\mu \mathrm{SR}$) results indicate that nearly half of the sample is magnetically ordered and spatially phase separated from the superconducting region. The transverse-field $\mu \mathrm{SR}$ results reveal that the superfluid density of $\mathrm{Li}({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}{)}_{0.2}{\mathrm{Fe}}_2{\mathrm{Se}}_2$ is two dimensional in nature. The temperature dependence of the penetration depth $\lambda (T)$ can be explained using a two-gap $s$-wave model. This implies that, despite the 2D nature of the superfluid density, the symmetry of the superconducting gap remains unaltered to the parent compound FeSe.

• Received 21 September 2012
• Publisher error corrected 5 April 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.137003