Coexistence of Clean- and Dirty-limit Superconductivity in LiFeAs

Abstract

The optical properties of LiFeAs with $T_c\simeq$ 18 K have been determined in the normal and superconducting states. The superposition of two Drude components yields a good description of the low-frequency optical response in the normal state. Below $T_c$, the optical conductivity reveals two isotropic superconducting gaps with ${\Delta }_1\simeq 2.9$ $\pm$ 0.2 meV and ${\Delta }_2\simeq 5.5$ $\pm$ 0.4 meV. A comparison between the superconducting-state Mattis-Bardeen and the normal-state Drude components, in combination with a spectral weight analysis, indicates that the spectral weight associated with a band which has a very small scattering rate is fully transferred to the superfluid weight upon the superconducting condensate. These observations provide clear evidence for the coexistence of clean- and dirty-limit superconductivity in LiFeAs.

6 pages, 4 figures, Supplementary Material available

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• Electron-boson spectral density function of correlated multiband systems obtained from optical data: Ba0.6K0.4Fe2As2 and LiFeAs
• Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors
• The Three-Dimensional Electronic Structure of LiFeAs: Strong-coupling Superconductivity and Topology in the Iron Pnictides
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Reentrant phases in electron-doped ${\text{EuFe}}_2{\text{As}}_2$: spin glass and superconductivity
• Constraints on the total coupling strength to bosons in iron based superconductors