Spectroscopic evidence of superconductivity pairing at 83 K in single-layer FeSe/SrTiO films.

Single-layer FeSe films grown on the SrTiO substrate (FeSe/STO) have attracted much attention because of their possible record-high superconducting critical temperature (T) and distinct electronic structures. However, it has been under debate on how high its T can really reach due to the inconsistency of the results from different measurements. Here we report spectroscopic evidence of superconductivity pairing at 83 K in single-layer FeSe/STO films. By preparing high-quality single-layer FeSe/STO films, we observe strong superconductivity-induced Bogoliubov back-bending bands that extend to rather high binding energy ~ 100 meV by high-resolution angle-resolved photoemission measurements. They provide a new definitive benchmark of superconductivity pairing that is directly observed up to 83 K. Moreover, we find that the pairing state can be further divided into two temperature regions. These results indicate that either T as high as 83 K is achievable, or there is a pseudogap formation from superconductivity fluctuation in single-layer FeSe/STO films.