Phase Diagram and High Temperature Superconductivity at 65 K in Tuning Carrier Concentration of Single-Layer FeSe Films

TLDR

Superconductivity in cuprates and Fe‑based materials emerges by doping or pressure to suppress antiferromagnetism, and this rich phase diagram is key to understanding the mechanisms and related physics. The study reports a phase diagram of single‑layer FeSe films on SrTiO3, mapping charge‑carrier concentration via annealing. The authors grow single‑layer FeSe on SrTiO3 and tune carrier density by annealing over a wide range. Annealing induces dramatic band‑structure changes, revealing two competing phases, and produces a record 65 K superconducting transition, demonstrating wide tunability and high‑Tc suitable for probing superconductivity mechanisms and quantum phenomena.

Abstract

Superconductivity in the cuprate superconductors and the Fe-based superconductors is realized by doping the parent compound with charge carriers, or by application of high pressure, to suppress the antiferromagnetic state. Such a rich phase diagram is important in understanding superconductivity mechanism and other physics in the Cu- and Fe-based high temperature superconductors. In this paper, we report a phase diagram in the single-layer FeSe films grown on SrTiO3 substrate by an annealing procedure to tune the charge carrier concentration over a wide range. A dramatic change of the band structure and Fermi surface is observed, with two distinct phases identified that are competing during the annealing process. Superconductivity with a record high transition temperature (Tc) at ~65 K is realized by optimizing the annealing process. The wide tunability of the system across different phases, and its high-Tc, make the single-layer FeSe film ideal not only to investigate the superconductivity physics and mechanism, but also to study novel quantum phenomena and for potential applications.