ARPES on Unusual Superconducting Properties of Single-Layer FeSe/SrTiO3 Films

Single-layer FeSe films grown on SrTiO3 substrates have attracted much attention because of their record high superconducting critical temperature and distinct electronic structure. Here we report MBE growth of very high-quality single-layer FeSe/STO films, and systematic investigations of their electronic structure and superconducting properties by high-resolution angle-resolved photoemission spectroscopy measurements. Two ellipse-like electron pockets are clearly resolved at one Brillouin zone corner and obvious band splitting is observed. The anisotropic superconducting gap along the Fermi surface is measured with high precision. In particular, we observe very strong superconductivity-induced band back-bending that extends to rather high binding energy. The implications of these observation on superconductivity mechanism of the single-layer FeSe/SrTiO3 films will be discussed.