Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO\(_3\) substrates

• Published in: arXiv.org 2016-02
• Main Authors: Wang, Y, Nakatsukasa, K, Rademaker, L, Berlijn, T, Johnston, S
• Format: Article
• Language: English
• Subjects: Electron phonon interactions; Electronic structure; Forward scattering; Momentum transfer; Multilayers; Phonons; Photoelectric emission; Spectroscopy; Spectrum analysis; Substrates; Superconductivity; Thin films
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1602.00656

Mono- and multilayer FeSe thin films grown on SrTiO\(_\mathrm{3}\) and BiTiO\(_\mathrm{3}\) 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 \({\bf q}\)) 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.