Abstract
A high-frequency optical phonon mode of SrTiO3 (STO) was found to assist the high-temperature superconductivity observed recently at the interface between monolayer FeSe and STO substrate. However, the origin of this mode is not clear. Through first-principles calculations, we find that there is a novel polar phonon mode on the surface layers of the STO substrate, which does not exist in the STO crystals. The oxygen vacancies near the FeSe/STO interface drives the dispersion of this phonon mode to be flat and lowers its energy, whereas the charge transfer between STO substrate and FeSe monolayer further reduces its energy to 81 meV. This energy is in good agreement with the experimental value fitted by Lee et al. for the phonon mode responsible for the observed replica band separations and the increased superconducting gap. The oxygen-vacancy-induced flat and polar phonon mode provides clues for understanding the origin of high Tc superconductivity at the FeSe/STO interface.
Highlights
A high-frequency optical phonon mode of SrTiO3 (STO) was found to assist the high-temperature superconductivity observed recently at the interface between monolayer FeSe and STO substrate
In monolayer FeSe on STO substrate, each energy band of the FeSe film is exactly replicated at a fixed energy separation, which is observed by ARPES2
In this paper, based on the first principles calculations, we have carefully studied the vibrational properties of the FeSe/STO interface, and successfully identify a special phonon mode, which is strongly related to the oxygen vacancy on STO surface and the charge transfer between the FeSe monolayer and STO substrate
Summary
A high-frequency optical phonon mode of SrTiO3 (STO) was found to assist the high-temperature superconductivity observed recently at the interface between monolayer FeSe and STO substrate. The oxygen vacancies near the FeSe/STO interface drives the dispersion of this phonon mode to be flat and lowers its energy, whereas the charge transfer between STO substrate and FeSe monolayer further reduces its energy to 81 meV This energy is in good agreement with the experimental value fitted by Lee et al for the phonon mode responsible for the observed replica band separations and the increased superconducting gap. The interaction between FeSe electrons and the particular STO phonon mode is believed to strengthen the Cooper pairing[20] and be responsible for enlarging the superconducting gap in the single-layer FeSe/STO system It is so far not clear how the FeSe monolayer and the STO phonon mode coupled with each other, or why the experimentally observed replica bands appear. The calculated energy of the phonon mode is in accordance with the recent observed particular surface phonon mode, which is very different from bulk STO
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
