Aspects of forward scattering in FeSe thin films

Last year we showed that you get ridiculously high superconducting temperatures if the electron-phonon coupling is strongly peaked around zero momentum transfer, so-called forward scattering. While the paper from that time is just accepted in the New Journal of Physics, we came up with a new paper discussing many of the more subtle details – for example about the vertex corrections, quasiparticle interference and gap structure. This week on the arXiv!

(PS: I’ve updated the publication list, a lot of things from last year are now peer-reviewed published somewhere, such as our MBL-paper in Physical Review Letters, or the topological classification in Phys. Rev. B!)

Title: Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO3 substrates

Y. Wang, K. Nakatsukasa, L. Rademaker, T. Berlijn, and S. Johnston


Abstract: Mono- and multilayer FeSe thin films grown on SrTiO3 and BiTiO3 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 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 e-ph interaction is peaked at small momentum transfer and in the FeSe/STO system.


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