Spectroscopic evidence of superconductivity pairing at 83\u2009K in single-layer FeSe/SrTiO3 films

Yuan Huang,Cong Li,Hongtao Yan,Hongtao Rong,Chaohui Yin,X. J. Zhou,Lin Zhao,Hao Chen,Dingsong Wu,Qiang Gao,Zhihai Zhu,Yong Hu,Jianwei Huang,Yu Xu,Yongqing Cai,Zuyan Xu,Guodong Liu,Qingyan Wang

doi:10.1038/s41467-021-23106-y

Abstract

Single-layer FeSe films grown on the SrTiO3 substrate (FeSe/STO) have attracted much attention because of their possible record-high superconducting critical temperature (Tc) and distinct electronic structures. However, it has been under debate on how high its Tc 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 Tc as high as 83 K is achievable, or there is a pseudogap formation from superconductivity fluctuation in single-layer FeSe/STO films.

Highlights

We prepared high-quality single-layer FeSe/STO films that make it possible to resolve clearly the band splitting and in particular the superconductivity-induced Bogoliubov backbending bands from the high-resolution ARPES measurements
In ARPES measurements on FeSe-related superconductors, AxFe2−ySe2 (A = K, Rb, Cs, Tl and etc.) superconductors with a Tc ~32 K36–38 and (Li, Fe)OHFeSe superconductor with a Tc of 42 K26, the gap opening temperatures are consistent with the transport and magnetic Tc, indicating no pseudogap formation in these superconductors
The transport measurement on singlelayer FeSe/STO films is challenging because the samples are fragile that can be damaged when exposed to air

Summary

Introduction

We prepared high-quality single-layer FeSe/STO films that make it possible to resolve clearly the band splitting and in particular the superconductivity-induced Bogoliubov backbending bands from the high-resolution ARPES measurements. The Bogoliubov back-bending bands provide a decisive signature of superconductivity pairing. We have identified an indication of superconductivity pairing at 83 K directly from the Bogoliubov back-bending bands in single-layer FeSe/STO films. Actual long-range pairing is realized in both regions. The identification of superconductivity pairing at 83 K in single-layer FeSe/ STO films is significant because it either indicates that Tc as high as 83 K is achievable in iron-based superconductors, or it provides spectroscopic evidence on the existence of pseudogap in single-layer FeSe/STO films, making it similar to high temperature cuprate superconductor

Methods

Results

Conclusion