Identification of a large amount of excess Fe in superconducting single-layer FeSe/SrTiO3 films
Yong Hu, Yu Xu, Qingyan Wang, Lin Zhao, Shaolong He, Jianwei Huang, Cong Li, Guodong Liu, X. J. Zhou
DOI 10.1103/PhysRevB.97.224512 · Physical Review B
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Abstract
Single-layer FeSe films grown on SrTiO3 (STO) substrates have attracted much attention because of their record high superconducting critical temperature TC. It is generally believed that the composition of the epitaxially grown single-layer FeSe/STO films is stoichiometric; that is, the ratio of Fe to Se is 1:1. Here we report the identification of a large amount of excess Fe in superconducting single-layer FeSe/STO films. By depositing Se onto superconducting single-layer FeSe/STO films, we find by in situ scanning tunneling microscopy the formation of second-layer FeSe islands on top of the first layer during the annealing process at a surprisingly low temperature (∼150∘C) which is much lower than the usual growth temperature (∼490∘C). This observation is used to detect excess Fe and estimate its quantity in single-layer FeSe/STO films. The amount of excess Fe detected is at least 20%, which is surprisingly high for superconducting single-layer FeSe/STO films. The discovery of such a large amount of excess Fe should be taken into account in understanding the high-TC superconductivity and points to a likely route to further enhance TC in superconducting single-layer FeSe/STO films.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| FeSe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 60 | Pressure not reported | onset |
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