Superconductivity enhancement in FeSe/SrTiO₃: a review from the perspective of electron–phonon coupling

Abstract

Single-layer FeSe lms grown on SrTiO 3 , with the highest superconducting transition temperature (T C ) among all the iron-based superconductors, serves as an ideal platform for studying the microscopic mechanisms of high-T C superconductivity. The signi cant role of interfacial coupling has been widely recognized, while the precise nature of the T C enhancement remains open. In this review, we focus on the investigations of the interfacial coupling in FeSe/SrTiO 3 from the perspective of electron-phonon coupling (EPC). The main content will include an overview of the experimental measurements associated with different theoretical models and arguments about the EPC. Especially, besides the discussions of EPC based on the measurements of electronic states, we will emphasize the analyses based on phonon measurements. A uniform picture about the nature of the EPC and its relation to the T C enhancement in FeSe/SrTiO 3 has still not achieved, which should be the key for further studies aiming to the in-depth understanding of high-T C superconductivity and the discovery of new superconductors with even enhanced T C .

On the Remarkable Superconductivity of FeSe and Its Close Cousins

“…A potentially important clue to the physics of these systems, and the influence of the substrate, was found in ARPES measurements [272], which identified in second derivative spectra clear "replica bands", "shadow" copies of bands both at Γ and M shifted rigidly downward in energy by ∼100 meV. These experiments, along with others reviewed recently in reference [286], were interpreted by the authors of reference [272] as implying the presence of a strong interaction of FeSe electrons with phonons, probably originating from the substrate. It was furthermore argued that the electron-phonon interaction must be rather strongly peaked in the forward direction q = 0 to explain this observation.…”

LaO as a candidate substrate for realizing superconductivity in an FeSe epitaxial film

“…To explore the superconducting mechanism of FeSe/STO, many experimental and theoretical studies have been performed [18][19][20][21][22][23] . Some have focused on the charge degree of freedom.…”