How Correlated is the FeSe/SrTiO_{3} System?

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Monolayer FeSe exhibits a significantly higher critical temperature (∼10x) compared to its bulk phase.
• The electronic structure of monolayer FeSe differs from its bulk counterpart, prompting further investigation.
• SrTiO3 serves as a substrate for monolayer FeSe, potentially influencing its properties.

Purpose of the Study:

• To investigate the effects of electronic correlations on the atomic geometry and electronic structure of monolayer FeSe on SrTiO3.
• To understand the role of the Se-Fe-Se angle and correlation strength (Hund's J vs. Hubbard U) in monolayer FeSe.
• To explore the impact of electron doping via oxygen vacancies in SrTiO3 on the electronic correlations.

Main Methods:

• Combined density functional theory (DFT) and dynamical mean-field theory (DMFT) calculations.
• Analysis of atomic-scale geometry and electronic structure.
• Investigation of temperature-dependent electronic properties.

Main Results:

• Electronic correlations significantly affect the atomic geometry and electronic structure of monolayer FeSe.
• Se-Fe-Se angle is a dominant factor controlling correlations, with increased sensitivity in the monolayer.
• Correlations are more dependent on Hund's J than Hubbard U, consistent with Hund's metallic behavior.

Conclusions:

• Electronic correlations play a crucial role in the unique properties of monolayer FeSe.
• The Hund's metallic nature is confirmed by the observed orbital selective crossover.
• Electron doping in SrTiO3 enhances correlation strength, particularly in the dxy orbital, by modifying the Se-Fe-Se angle.