Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films

The recent discovery of possible high-temperature superconductivity

in single-layer FeSe films1,2 has generated significant

experimental and theoretical interest3,4

. In both the cuprate5,6

and the iron-based7–11 high-temperature superconductors, superconductivity

is induced by doping charge carriers into the

parent compound to suppress the antiferromagnetic state. It is

therefore important to establish whether the superconductivity

observed in the single-layer sheets of FeSe—the essential

building blocks of the Fe-based superconductors—is realized

by undergoing a similar transition. Here we report the phase

diagram for an FeSe monolayer grown on a SrTiO3 substrate,

by tuning the charge carrier concentration over a wide range

through an extensive annealing procedure. We identify two

distinct phases that compete during the annealing process:

the electronic structure of the phase at low doping (N phase)

bears a clear resemblance to the antiferromagnetic parent

compound of the Fe-based superconductors, whereas the superconducting

phase (S phase) emerges with the increase in

doping and the suppression of the N phase. By optimizing

the carrier concentration, we observe strong indications of

superconductivity with a transition temperature of 65 ± 5 K.

The wide tunability of the system across different phases

makes the FeSe monolayer ideal for investigating not only

the physics of superconductivity, but also for studying novel

quantum phenomena more generally.