Observation of high-Tc superconductivity in rectangular FeSe/SrTiO3(110) monolayers.

We design a monolayer film of FeSe on SrTiO3(110) substrate [FeSe/STO(110)], with a C2 symmetry induced by epitaxial strain. Compared to FeSe on SrTiO3(001) substrate [FeSe/STO(001)], one of the in-plane lattice constants is reduced by 6%, to ~3.67 Å. FeSe/STO(110) exhibits a large nearly isotropic superconducting gap of 16 meV filled around 60 K, similar to those obtained on FeSe/STO(001) films. Our results strongly suggest that the lattice C4 symmetry is not essential for reaching high Tc's in Fe-based superconductors and pose a new challenge to theory. [ABSTRACT FROM AUTHOR]