Anomalous correlation effects and unique phase diagram of electron doped FeSe revealed by angle resolved photoemission spectroscopy

TL;DR

This study maps the phase diagram of electron-doped FeSe using ARPES, revealing a unique doping-dependent evolution of phases, including a superconducting dome with a maximum Tc of 44K, distinct from other Fe-based superconductors.

Contribution

It provides the first comprehensive phase diagram of electron-doped FeSe, highlighting the doping-dependent correlation strength and the emergence of an insulating phase in heavily overdoped samples.

Findings

Correlation strength increases with doping

Superconductivity peaks at 44K in a dome-shaped phase region

An insulating phase appears in heavily overdoped FeSe

Abstract

In FeSe-derived superconductors, the lack of a systematic and clean control on the carrier concentration prevents the comprehensive understanding on the phase diagram and the interplay between different phases. Here by K dosing and angle resolved photoemission study on thick FeSe films and FeSe$_{0.93}$S$_{0.07}$ bulk crystals, the phase diagram of FeSe as a function of electron doping is established, which is extraordinarily different from other Fe-based superconductors. The correlation strength remarkably increases with increasing doping, while an insulting phase emerges in the heavily overdoped regime. Between the nematic phase and the insulating phase, a dome of enhanced superconductivity is observed, with the maximum superconducting transition temperature of 44$\pm$2~K. The enhanced superconductivity is independent of the thickness of FeSe, indicating that it is intrinsic to FeSe. Our findings provide an ideal system with variable doping for understanding the different phases and rich physics in the FeSe family.