Soft phonons in the interface layer of the STO substrate can explain high temperature superconductivity in one unit cell FeSe

Abstract

Using a microscopic model of lattice vibrations in the STO(001) substrate, an additional Ωs = 50mev longitudinal optical (LO) interface mode is identified. The soft mode propagating mainly in the first T iO2 layer ("O chains") has stronger electron -phonon coupling to electron gas in F eSe than a well known Ω h = 100mev hard mode. The coupling constant, critical temperature, replica band are calculated. Although there exists a forward in the electron -phonon scattering peak, it is clearly not as sharp as assumed in recent theories (delta function -like). The critical temperature is obtained by solution of the gap equation and agrees with the observed one. The corresponding electron phonon coupling constant λ = 0.23. The quasiparticle normal state "satellite" in spectral weight is broad and its peak appears at frequency much higher than Ωs consistent with observations usually associated with Ω h . Possible relation of the transversal counterpart of the surface LO soft mode with known phonons is discussed.