  The high temperature superconductivity in single-unit-cell (1UC) FeSe on
SrTiO3 (STO)(001) and the observation of replica bands by angle-resolved
photoemission spectroscopy (ARPES) have led to the conjecture that the coupling
between FeSe electron and the STO phonon is responsible for the enhancement of
Tc over other FeSe-based superconductors1,2. However the recent observation of
a similar superconducting gap in FeSe grown on the (110) surface of STO raises
the question of whether a similar mechanism applies3,4. Here we report the
ARPES study of the electronic structure of FeSe grown on STO(110). Similar to
the results in FeSe/STO(001), clear replica bands are observed. We also present
a comparative study of STO (001) and STO(110) bare surfaces, where photo doping
generates metallic surface states. Similar replica bands separating from the
main band by approximately the same energy are observed, indicating this
coupling is a generic feature of the STO surfaces and interfaces. Our findings
suggest that the large superconducting gaps observed in FeSe films grown on two
different STO surface terminations are likely enhanced by a common coupling
between FeSe electrons and STO phonons.
