Measurement of Coherent Polarons in the Strongly Coupled Antiferromagnetically Ordered Iron-ChalcogenideFe1.02Teusing Angle-Resolved Photoemission Spectroscopy

The nature of metallicity and the level of electronic correlations in the antiferromagnetically ordered parent compounds are two important open issues for the iron-based superconductivity. We perform a temperature-dependent angle-resolved photoemission spectroscopy study of ${\mathrm{Fe}}_{1.02}\mathrm{Te}$, the parent compound for iron chalcogenide superconductors. Deep in the antiferromagnetic state, the spectra exhibit a ``peak-dip-hump'' line shape associated with two clearly separate branches of dispersion, characteristics of polarons seen in manganites and lightly doped cuprates. As temperature increases towards the N\'eel temperature (${T}_{N}$), we observe a decreasing renormalization of the peak dispersion and a counterintuitive sharpening of the hump linewidth, suggestive of an intimate connection between the weakening electron-phonon ($e$-ph) coupling and antiferromagnetism. Our finding points to the highly correlated nature of the ${\mathrm{Fe}}_{1.02}\mathrm{Te}$ ground state featured by strong interactions among the charge, spin, and lattice and a good metallicity plausibly contributed by the coherent polaron motion.