Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO${}_3$ substrates

Abstract

Mono- and multilayer FeSe thin films grown on SrTiO${}_3$ and BiTiO${}_3$ substrates exhibit a greatly enhanced superconductivity over that found in bulk FeSe. A number of proposals have been advanced for the mechanism of this enhancement. One possibility is the introduction of a cross-interface electron-phonon ($e$-$ph$) interaction between the FeSe electrons and oxygen phonons in the substrates that is peaked in the forward scattering (small $\mathbf{q}$) direction due to the two-dimensional nature of the interface system. Motivated by this, we explore the consequences of such an interaction on the superconducting state and electronic structure of a two-dimensional system using Migdal-Eliashberg theory. This interaction produces not only deviations from the expectations of conventional phonon-mediated pairing but also replica structures in the spectral function and density of states, as probed by angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and quasi-particle interference imaging. We also discuss the applicability of Migdal-Eliashberg theory for a situation where the \ep interaction is peaked at small momentum transfer and in the FeSe/STO system.

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• Emergence of Frohlich polaron from interlayer electron-phonon coupling in van der Waals heterostructure
• Phonon dispersion and the competition between pairing and charge order
• High Tc via spin fluctuations from incipient bands: application to monolayers and intercalates of FeSe
• Superconductivity in FeSe thin films driven by the interplay between nematic fluctuations and spin-orbit coupling
• Electron phonon coupling versus photoelectron energy loss at the origin of replica bands in photoemission of FeSe on SrTiO${}_3$
• Langevin Simulations of a Long Range Electron Phonon Model
• Full-bandwidth Eliashberg theory of superconductivity beyond Migdal's approximation
• Multiband full-bandwidth anisotropic Eliashberg theory of interfacial electron-phonon coupling and high-T${}_c$ superconductivity in FeSe/SrTiO${}_3$
• Correlation of Fe-based Superconductivity and Electron-Phonon Coupling in an FeAs/Oxide Heterostructure
• Interfacial Electron-Phonon Coupling Constants Extracted from Intrinsic Replica Bands in Monolayer FeSe/SrTiO${}_3$
• Unconventional pairing in single FeSe layers
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• Optimal Boson energy for superconductivity in the Holstein model
• The phonon mechanism explanation of the superconductivity dichotomy between FeSe and FeS monolayers on STO and other substrates
• Understanding and enhancing superconductivity in FeSe/STO by quantum size effects
• Non-thermal pairing glue of electrons in the steady state