Measurement of Coherent Polarons in the Strongly Coupled Antiferromagnetically Ordered Iron-Chalcogenide Fe1.02Te using Angle-Resolved Photoemission Spectroscopy

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal polaron features and strong electron-phonon interactions in Fe1.02Te, shedding light on its correlated electronic ground state and metallicity in the antiferromagnetic phase.

Contribution

It provides the first direct observation of coherent polarons in Fe1.02Te and links electron-phonon coupling to antiferromagnetic order in iron chalcogenides.

Findings

Observation of peak-dip-hump line shape indicating polarons

Decrease in dispersion renormalization with temperature

Sharpening of hump linewidth near Neel temperature

Abstract

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 Fe1.02Te, 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 Neel 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 Fe1.02Te ground state featured by strong interactions among the charge, spin and lattice and a good metallicity plausibly contributed by the coherent polaron motion.