The Role of SrTiO3 Phonon Penetrating into thin FeSe Films in the Enhancement of Superconductivity

Abstract

The significant role of interfacial coupling on the superconductivity enhancement in FeSe films on SrTiO3 has been widely recognized. But the explicit origination of this coupling is yet to be identified. Here by surface phonon measurements using high resolution electron energy loss spectroscopy, we found electric field generated by Fuchs-Kliewer (F-K) phonon modes of SrTiO3 can penetrate into FeSe films and strongly interact with electrons therein. The mode-specific electron-phonon coupling (EPC) constant for the ~92 meV F-K phonon is ~0.25 in the single-layer FeSe on SrTiO3. With increasing FeSe thickness, the penetrating field intensity decays exponentially, which matches well the observed exponential decay of the superconducting gap. It is unambiguously shown that the SrTiO3 F-K phonon penetrating into FeSe is essential in the interfacial superconductivity enhancement.

Main text: 6 pages, 3 figures; Supplementary Material: 8 pages, 6 figures. An error in the EPC constant calculation was corrected in this version and several new references are added. The authors would like to thank Dr. Yan Wang (University of Tennessee) for pointing out the error

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• Computation and data driven discovery of topological phononic materials
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• Dynamic interfacial polaron enhanced superconductivity of FeSe/SrTiO3
• High-temperature superconductivity in one-unit-cell FeSe films
• Interface high-temperature superconductivity
• Electron phonon coupling versus photoelectron energy loss at the origin of replica bands in photoemission of FeSe on SrTiO${}_3$
• Ultrafast Quasiparticle Dynamics and Electron-Phonon Coupling in (Li0.84Fe0.16)OHFe0.98Se
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• Dual Enhancement of Superconductivity in FeSe/SrTiO3 via Orbital and Correlation Synergy
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