Phonon-plasmonic bipolaronic superconductivity in the FeSe/SrTiO3 quantum structure

Abstract

The bipolaron mechanism of experimentally observed high-temperature superconductivity (HTSC) in FeSe monolayers on massive SrTiO3 substrates [1] has been theoretically investigated, based on the exact Hamiltonian of the electron-phonon interaction for multilayer structures [2]. Bipolaronic states arise in FeSe quantum layers due to the interaction of electrons with the electric field of Fuchs-Kliewer surface optical phonons [3] of the strongly polar semiconductor SrTiO3 penetrating into the FeSe monolayer. The effect of doping of a crystalline SrTiO3 substrate with n-type niobium impurities on the critical temperature 𝑇𝑐 of HTSC in a monolayer of FeSe is considered. The role of surface polaron plasmons formed in SrTiO3 upon contact with the FeSe quantum layer during the interaction of impurity electrons with surface optical phonons of SrTiO3 is investigated. It is shown that electrons in the quasi-two-dimensional FeSe layer induce an additional polarization potential in the SrTiO3 substrate, which increases the binding energy of bipolarons in the FeSe layer, which leads to an increase in the critical temperature of bipolaronic superconductivity.