Picoscale structural insight into superconductivity of monolayer FeSe/SrTiO₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Monolayer (ML) FeSe films on SrTiO3 substrates exhibit enhanced superconducting transition temperatures (Tc).
• The atomic structure of the FeSe/SrTiO3 interface significantly influences magnetic properties and interfacial electron-phonon interactions, key to high-Tc superconductivity.

Purpose of the Study:

• To resolve the atomic-scale structure of the FeSe/SrTiO3 interface.
• To establish a structural framework for understanding the high-Tc mechanism in this system.

Main Methods:

• Complementary analysis using scanning transmission electron microscopy (STEM).
• In situ surface X-ray diffraction (SXRD) for atomic-scale structural determination.

Main Results:

• Identified a specific interface registration with stronger bonding, leading to coherently strained ML FeSe.
• Determined key structural parameters: ML FeSe-oxide distance, Se-Fe-Se bond angles, layer-resolved Fe-Se distances, and FeSe lattice registry relative to the oxide.

Conclusions:

• Detailed picoscale structural determination of the FeSe/SrTiO3 interface has been achieved.
• This provides an explicit structural framework and constraints for theoretical models investigating the high-Tc superconductivity mechanism.