Enhancement of effective masses of the surface polaron in FeSe thin film on SrTiO3 substrate

Abstract We study the correction of the effective mass of the surface polaron in monolayer FeSe on SrTiO 3 substrate using a variational approach, in which surface polaron states are formed arising from the coupling between electrons in FeSe film and two kinds of surface optical (SO) phonon modes in SrTiO 3 substrate. We give a concise formula for the relations of the effective masses with the electron–SO phonon coupling matrixes, and find that the effective masses are enhanced significantly due to these coupling, which are very good agreement with the recent experimental measurements. Moreover, the effective masses depend strongly on the cutoff wave vectors of SO phonon modes and the interlayer distance between FeSe and SrTiO 3 substrate. Our theoretical results provide a practical route to analyze the electron–SO phonon coupling by measuring the variation of effective masses in experiments.