Polaronic behavior in highly two-dimensional iron-based superconductor Ca₁₀(Pt₃As₈)(Fe_1-xPt_xAs)₁₀

In the phase diagram of Ca₁₀(Pt₃As₈)(Fe_1-xPt_xAs)₁₀, above the superconducting (SC) and antiferromagnetic (AFM) dome, there exists a semiconducting-like behavior, which mimics the pseudogap in cuprates. Investigating the origin of this behavior would provide us an important clue for the pairing mechanism. In this work, we have synthesized the parent compound and the optimal doped Ca₁₀(Pt₃As₈)(Fe_1-xPt_xAs)₁₀ and measured their optical properties. From their optical conductivity, we found that the diminishing of the low-energy spectral weight in the normal state, corresponding to the semiconducting-like behavior, is related to the AFM fluctuation. Furthermore, we’ve realized the magnetic-enhanced electron-phonon coupling and that the far-infrared absorption peak in the optimal doped sample could be well described by the large polaron model, indicating the formation of large polaron in the semiconducting dome. Below Tc~12K, the polaron peak collapsed into the superfluid. Thus, we propose that the magnetism induced polaron may contribute the unconventional pairing.