Peculiarities of superconductivity in the single-layer FeSe/SrTiO3 interface

摘要

Observation of replica bands in the angle-resolved photoemission spectroscopy (ARPES) spectra of single-layer FeSe on a strontium titanate substrate revealed a phonon component contribution to mechanisms behind its high-T-c superconductivity. We study the interaction of the in-layer FeSe electrons with the electric potential of the longitudinal (LO) modes at the surface of bulk SrTiO3. A two-dimensional system of charges at the FeSe/SrTiO3 interface includes both the itinerant and the immobile electrons. The latter significantly change the interface characteristics, increasing screening at the substrate surface and thereby reducing the strength of the electron-LO-phonon interaction. In what follows, the dielectric constant serves as a free parameter and is determined using the ARPES measurements of the replicas. Two-dimensional Coulomb screening is accounted for in the random-phase approximation. It is shown that the model is applicable over the entire range of the parameters typical for current experiments. The estimates from this model make possible the conclusion that the LO-phonon-mediated pairing alone cannot account for the temperatures of the superconducting transitions T-c in the single-layer FeSe/SrTiO3 reported in these experiments. This does not exclude that the LO-phonon mechanisms can become more significant in differently and better prepared single-layer FeSe films. Available experiments are briefly discussed. Thus far no measurements exist on the dependence of T-c on the concentration of electrons doped into the in-layer FeSe band.