Yuan-Yuan Xiang, Fa Wang, Da Wang, Qiang-Hua Wang, Dung-Hai Lee
In a recent experiment the superconducting gap of a single unit cell thick
FeSe film on SrTiO$_3$ substrate is observed by scanning tunnelling
spectroscopy. Interestingly the value of the gap is about an order of magnitude
larger than that of the bulk FeSe. In this paper we study the effects of
interaction between the electrons and the soft phonons of SrTiO$_3$ on the
$T_c$ of the FeSe/SrTiO$_3$ interface superconductor. By solving the
phenomenological Eliashberg equations and performing the singular mode
functional renormalization group calculation on the electron-phonon system, we
conclude that the soft phonons of SrTiO$_3$ can significantly change the
pairing scale and even the pairing symmetry in FeSe/SrTiO$_3$. We propose this
as the mechanism of the observed $T_c$ enhancement and comment on the possible
signatures of electron-phonon (e-ph) coupling. Our results raise the concern
about whether the effect of phonons, especially the inter-pocket phonon, can be
ignored even for bulk iron-based superconductors.
View original:
http://arxiv.org/abs/1202.4141
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