Imaging the Electron-Boson Coupling in Superconducting FeSe

Abstract

Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a 'dip-hump' feature at energy Ω~ 4.7 kBTc beyond the superconducting gap Δ. Spectra on strained regions of the FeSe films reveal simultaneous decreases in Δand Ω. This contrasts with all previous reports on other high-Tc superconductors, where Δlocally anti-correlates with Ω. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.

5 pages, 4 figures

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• Interface enhanced electron-phonon coupling and high temperature superconductivity in potassium-coated ultra-thin FeSe films on SrTiO3
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• Electron carriers with possible Dirac-cone-like dispersion in FeSe${}_{1-x}$S${}_x$ ($x$ = 0 and 0.14) single crystals triggered by structural transition
• Interface high-temperature superconductivity
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• Emergence of an incipient ordering mode in FeSe
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• Correlation of Fe-based Superconductivity and Electron-Phonon Coupling in an FeAs/Oxide Heterostructure
• Detection of bosonic mode as a signature of magnetic excitation in one unit cell FeSe on SrTiO3
• Unusual temperature evolution of superconductivity in LiFeAs
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• Spectroscopic evidence of nematic fluctuations in LiFeAs
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